diff --git a/.gitignore b/.gitignore
index 94bed859d..1ed573622 100644
--- a/.gitignore
+++ b/.gitignore
@@ -32,6 +32,7 @@ env/
 *.swp
 *.swo
 .DS_Store
+*.tmp
 
 # Project specific
 *.log
diff --git a/README.md b/README.md
index 1c7dda215..53a837c55 100644
--- a/README.md
+++ b/README.md
@@ -61,7 +61,7 @@ specify init <PROJECT_NAME>
 specify check
 ```
 
-To upgrade specify run:
+To upgrade Specify, see the [Upgrade Guide](./docs/upgrade.md) for detailed instructions. Quick upgrade:
 
 ```bash
 uv tool install specify-cli --force --from git+https://github.com/github/spec-kit.git
@@ -205,7 +205,7 @@ specify init --here --ai copilot
 
 # Force merge into current (non-empty) directory without confirmation
 specify init . --force --ai copilot
-# or 
+# or
 specify init --here --force --ai copilot
 
 # Skip git initialization
diff --git a/docs/index.md b/docs/index.md
index 38a6de34e..a56fcc176 100644
--- a/docs/index.md
+++ b/docs/index.md
@@ -12,6 +12,7 @@ Spec-Driven Development **flips the script** on traditional software development
 
 - [Installation Guide](installation.md)
 - [Quick Start Guide](quickstart.md)
+- [Upgrade Guide](upgrade.md)
 - [Local Development](local-development.md)
 
 ## Core Philosophy
diff --git a/docs/toc.yml b/docs/toc.yml
index 082bb8c86..18650cb57 100644
--- a/docs/toc.yml
+++ b/docs/toc.yml
@@ -9,10 +9,11 @@
       href: installation.md
     - name: Quick Start
       href: quickstart.md
+    - name: Upgrade
+      href: upgrade.md
 
 # Development workflows
 - name: Development
   items:
     - name: Local Development
       href: local-development.md
-
diff --git a/docs/upgrade.md b/docs/upgrade.md
new file mode 100644
index 000000000..035706eb8
--- /dev/null
+++ b/docs/upgrade.md
@@ -0,0 +1,436 @@
+# Upgrade Guide
+
+> You have Spec Kit installed and want to upgrade to the latest version to get new features, bug fixes, or updated slash commands. This guide covers both upgrading the CLI tool and updating your project files.
+
+---
+
+## Quick Reference
+
+| What to Upgrade | Command | When to Use |
+|----------------|---------|-------------|
+| **CLI Tool Only** | `uv tool install specify-cli --force --from git+https://github.com/github/spec-kit.git` | Get latest CLI features without touching project files |
+| **Project Files** | `specify init --here --force --ai <your-agent>` | Update slash commands, templates, and scripts in your project |
+| **Both** | Run CLI upgrade, then project update | Recommended for major version updates |
+
+---
+
+## Part 1: Upgrade the CLI Tool
+
+The CLI tool (`specify`) is separate from your project files. Upgrade it to get the latest features and bug fixes.
+
+### If you installed with `uv tool install`
+
+```bash
+uv tool install specify-cli --force --from git+https://github.com/github/spec-kit.git
+```
+
+### If you use one-shot `uvx` commands
+
+No upgrade needed—`uvx` always fetches the latest version. Just run your commands as normal:
+
+```bash
+uvx --from git+https://github.com/github/spec-kit.git specify init --here --ai copilot
+```
+
+### Verify the upgrade
+
+```bash
+specify check
+```
+
+This shows installed tools and confirms the CLI is working.
+
+---
+
+## Part 2: Updating Project Files
+
+When Spec Kit releases new features (like new slash commands or updated templates), you need to refresh your project's Spec Kit files.
+
+### What gets updated?
+
+Running `specify init --here --force` will update:
+
+- ✅ **Slash command files** (`.claude/commands/`, `.github/prompts/`, etc.)
+- ✅ **Script files** (`.specify/scripts/`)
+- ✅ **Template files** (`.specify/templates/`)
+- ✅ **Shared memory files** (`.specify/memory/`) - **⚠️ See warnings below**
+
+### What stays safe?
+
+These files are **never touched** by the upgrade—the template packages don't even contain them:
+
+- ✅ **Your specifications** (`specs/001-my-feature/spec.md`, etc.) - **CONFIRMED SAFE**
+- ✅ **Your implementation plans** (`specs/001-my-feature/plan.md`, `tasks.md`, etc.) - **CONFIRMED SAFE**
+- ✅ **Your source code** - **CONFIRMED SAFE**
+- ✅ **Your git history** - **CONFIRMED SAFE**
+
+The `specs/` directory is completely excluded from template packages and will never be modified during upgrades.
+
+### Update command
+
+Run this inside your project directory:
+
+```bash
+specify init --here --force --ai <your-agent>
+```
+
+Replace `<your-agent>` with your AI assistant. Refer to this list of [Supported AI Agents](../README.md#-supported-ai-agents)
+
+**Example:**
+
+```bash
+specify init --here --force --ai copilot
+```
+
+### Understanding the `--force` flag
+
+Without `--force`, the CLI warns you and asks for confirmation:
+
+```
+Warning: Current directory is not empty (25 items)
+Template files will be merged with existing content and may overwrite existing files
+Proceed? [y/N]
+```
+
+With `--force`, it skips the confirmation and proceeds immediately.
+
+**Important: Your `specs/` directory is always safe.** The `--force` flag only affects template files (commands, scripts, templates, memory). Your feature specifications, plans, and tasks in `specs/` are never included in upgrade packages and cannot be overwritten.
+
+---
+
+## ⚠️ Important Warnings
+
+### 1. Constitution file will be overwritten
+
+**Known issue:** `specify init --here --force` currently overwrites `.specify/memory/constitution.md` with the default template, erasing any customizations you made.
+
+**Workaround:**
+
+```bash
+# 1. Back up your constitution before upgrading
+cp .specify/memory/constitution.md .specify/memory/constitution-backup.md
+
+# 2. Run the upgrade
+specify init --here --force --ai copilot
+
+# 3. Restore your customized constitution
+mv .specify/memory/constitution-backup.md .specify/memory/constitution.md
+```
+
+Or use git to restore it:
+
+```bash
+# After upgrade, restore from git history
+git restore .specify/memory/constitution.md
+```
+
+### 2. Custom template modifications
+
+If you customized any templates in `.specify/templates/`, the upgrade will overwrite them. Back them up first:
+
+```bash
+# Back up custom templates
+cp -r .specify/templates .specify/templates-backup
+
+# After upgrade, merge your changes back manually
+```
+
+### 3. Duplicate slash commands (IDE-based agents)
+
+Some IDE-based agents (like Kilo Code, Windsurf) may show **duplicate slash commands** after upgrading—both old and new versions appear.
+
+**Solution:** Manually delete the old command files from your agent's folder.
+
+**Example for Kilo Code:**
+
+```bash
+# Navigate to the agent's commands folder
+cd .kilocode/rules/
+
+# List files and identify duplicates
+ls -la
+
+# Delete old versions (example filenames - yours may differ)
+rm speckit.specify-old.md
+rm speckit.plan-v1.md
+```
+
+Restart your IDE to refresh the command list.
+
+---
+
+## Common Scenarios
+
+### Scenario 1: "I just want new slash commands"
+
+```bash
+# Upgrade CLI (if using persistent install)
+uv tool install specify-cli --force --from git+https://github.com/github/spec-kit.git
+
+# Update project files to get new commands
+specify init --here --force --ai copilot
+
+# Restore your constitution if customized
+git restore .specify/memory/constitution.md
+```
+
+### Scenario 2: "I customized templates and constitution"
+
+```bash
+# 1. Back up customizations
+cp .specify/memory/constitution.md /tmp/constitution-backup.md
+cp -r .specify/templates /tmp/templates-backup
+
+# 2. Upgrade CLI
+uv tool install specify-cli --force --from git+https://github.com/github/spec-kit.git
+
+# 3. Update project
+specify init --here --force --ai copilot
+
+# 4. Restore customizations
+mv /tmp/constitution-backup.md .specify/memory/constitution.md
+# Manually merge template changes if needed
+```
+
+### Scenario 3: "I see duplicate slash commands in my IDE"
+
+This happens with IDE-based agents (Kilo Code, Windsurf, Roo Code, etc.).
+
+```bash
+# Find the agent folder (example: .kilocode/rules/)
+cd .kilocode/rules/
+
+# List all files
+ls -la
+
+# Delete old command files
+rm speckit.old-command-name.md
+
+# Restart your IDE
+```
+
+### Scenario 4: "I'm working on a project without Git"
+
+If you initialized your project with `--no-git`, you can still upgrade:
+
+```bash
+# Manually back up files you customized
+cp .specify/memory/constitution.md /tmp/constitution-backup.md
+
+# Run upgrade
+specify init --here --force --ai copilot --no-git
+
+# Restore customizations
+mv /tmp/constitution-backup.md .specify/memory/constitution.md
+```
+
+The `--no-git` flag skips git initialization but doesn't affect file updates.
+
+---
+
+## Using `--no-git` Flag
+
+The `--no-git` flag tells Spec Kit to **skip git repository initialization**. This is useful when:
+
+- You manage version control differently (Mercurial, SVN, etc.)
+- Your project is part of a larger monorepo with existing git setup
+- You're experimenting and don't want version control yet
+
+**During initial setup:**
+
+```bash
+specify init my-project --ai copilot --no-git
+```
+
+**During upgrade:**
+
+```bash
+specify init --here --force --ai copilot --no-git
+```
+
+### What `--no-git` does NOT do
+
+❌ Does NOT prevent file updates
+❌ Does NOT skip slash command installation
+❌ Does NOT affect template merging
+
+It **only** skips running `git init` and creating the initial commit.
+
+### Working without Git
+
+If you use `--no-git`, you'll need to manage feature directories manually:
+
+**Set the `SPECIFY_FEATURE` environment variable** before using planning commands:
+
+```bash
+# Bash/Zsh
+export SPECIFY_FEATURE="001-my-feature"
+
+# PowerShell
+$env:SPECIFY_FEATURE = "001-my-feature"
+```
+
+This tells Spec Kit which feature directory to use when creating specs, plans, and tasks.
+
+**Why this matters:** Without git, Spec Kit can't detect your current branch name to determine the active feature. The environment variable provides that context manually.
+
+---
+
+## Troubleshooting
+
+### "Slash commands not showing up after upgrade"
+
+**Cause:** Agent didn't reload the command files.
+
+**Fix:**
+
+1. **Restart your IDE/editor** completely (not just reload window)
+2. **For CLI-based agents**, verify files exist:
+   ```bash
+   ls -la .claude/commands/      # Claude Code
+   ls -la .gemini/commands/       # Gemini
+   ls -la .cursor/commands/       # Cursor
+   ```
+3. **Check agent-specific setup:**
+   - Codex requires `CODEX_HOME` environment variable
+   - Some agents need workspace restart or cache clearing
+
+### "I lost my constitution customizations"
+
+**Fix:** Restore from git or backup:
+
+```bash
+# If you committed before upgrading
+git restore .specify/memory/constitution.md
+
+# If you backed up manually
+cp /tmp/constitution-backup.md .specify/memory/constitution.md
+```
+
+**Prevention:** Always commit or back up `constitution.md` before upgrading.
+
+### "Warning: Current directory is not empty"
+
+**Full warning message:**
+```
+Warning: Current directory is not empty (25 items)
+Template files will be merged with existing content and may overwrite existing files
+Do you want to continue? [y/N]
+```
+
+**What this means:**
+
+This warning appears when you run `specify init --here` (or `specify init .`) in a directory that already has files. It's telling you:
+
+1. **The directory has existing content** - In the example, 25 files/folders
+2. **Files will be merged** - New template files will be added alongside your existing files
+3. **Some files may be overwritten** - If you already have Spec Kit files (`.claude/`, `.specify/`, etc.), they'll be replaced with the new versions
+
+**What gets overwritten:**
+
+Only Spec Kit infrastructure files:
+- Agent command files (`.claude/commands/`, `.github/prompts/`, etc.)
+- Scripts in `.specify/scripts/`
+- Templates in `.specify/templates/`
+- Memory files in `.specify/memory/` (including constitution)
+
+**What stays untouched:**
+
+- Your `specs/` directory (specifications, plans, tasks)
+- Your source code files
+- Your `.git/` directory and git history
+- Any other files not part of Spec Kit templates
+
+**How to respond:**
+
+- **Type `y` and press Enter** - Proceed with the merge (recommended if upgrading)
+- **Type `n` and press Enter** - Cancel the operation
+- **Use `--force` flag** - Skip this confirmation entirely:
+  ```bash
+  specify init --here --force --ai copilot
+  ```
+
+**When you see this warning:**
+
+- ✅ **Expected** when upgrading an existing Spec Kit project
+- ✅ **Expected** when adding Spec Kit to an existing codebase
+- ⚠️ **Unexpected** if you thought you were creating a new project in an empty directory
+
+**Prevention tip:** Before upgrading, commit or back up your `.specify/memory/constitution.md` if you customized it.
+
+### "CLI upgrade doesn't seem to work"
+
+Verify the installation:
+
+```bash
+# Check installed tools
+uv tool list
+
+# Should show specify-cli
+
+# Verify path
+which specify
+
+# Should point to the uv tool installation directory
+```
+
+If not found, reinstall:
+
+```bash
+uv tool uninstall specify-cli
+uv tool install specify-cli --from git+https://github.com/github/spec-kit.git
+```
+
+### "Do I need to run specify every time I open my project?"
+
+**Short answer:** No, you only run `specify init` once per project (or when upgrading).
+
+**Explanation:**
+
+The `specify` CLI tool is used for:
+- **Initial setup:** `specify init` to bootstrap Spec Kit in your project
+- **Upgrades:** `specify init --here --force` to update templates and commands
+- **Diagnostics:** `specify check` to verify tool installation
+
+Once you've run `specify init`, the slash commands (like `/speckit.specify`, `/speckit.plan`, etc.) are **permanently installed** in your project's agent folder (`.claude/`, `.github/prompts/`, etc.). Your AI assistant reads these command files directly—no need to run `specify` again.
+
+**If your agent isn't recognizing slash commands:**
+
+1. **Verify command files exist:**
+   ```bash
+   # For GitHub Copilot
+   ls -la .github/prompts/
+
+   # For Claude
+   ls -la .claude/commands/
+   ```
+
+2. **Restart your IDE/editor completely** (not just reload window)
+
+3. **Check you're in the correct directory** where you ran `specify init`
+
+4. **For some agents**, you may need to reload the workspace or clear cache
+
+**Related issue:** If Copilot can't open local files or uses PowerShell commands unexpectedly, this is typically an IDE context issue, not related to `specify`. Try:
+- Restarting VS Code
+- Checking file permissions
+- Ensuring the workspace folder is properly opened
+
+---
+
+## Version Compatibility
+
+Spec Kit follows semantic versioning for major releases. The CLI and project files are designed to be compatible within the same major version.
+
+**Best practice:** Keep both CLI and project files in sync by upgrading both together during major version changes.
+
+---
+
+## Next Steps
+
+After upgrading:
+
+- **Test new slash commands:** Run `/speckit.constitution` or another command to verify everything works
+- **Review release notes:** Check [GitHub Releases](https://github.com/github/spec-kit/releases) for new features and breaking changes
+- **Update workflows:** If new commands were added, update your team's development workflows
+- **Check documentation:** Visit [github.io/spec-kit](https://github.github.io/spec-kit/) for updated guides