Follow the next steps to upgrade from Xcode4 or Xcode5 DP to the now released Xcode5 GM. Be sure to trash any DP or it won’t work.

Update: Step 3 and 8 are no longer required for Titanium Studio to recognize Xcode as being properly installed set up.

1. Download Xcode5 GM from the iOS Dev Center and open the DMG.
2. Move any earlier Xcode5 Developer Preview (like Xcode5-DP6) release to the trash.
3. Backup the iOS 6.1 SDK packaged within your current Xcode4 installation to your Desktop:
   cp -r /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS6.1.sdk ~/Desktop/
4. Drag the Xcode5 GM release (Xcode) to Applications, overwriting any current Xcode 4 installation.
5. Open Xcode to accept the license and finish configuration.
6. Install the command-line tools via Xcode > Preferences > Downloads.
7. Make sure the command-line tools have the proper Xcode version selected:
   sudo xcode-select -switch /Applications/Xcode.app/Contents/Developer
8. Restore the iOS 6.1 SDK into the new Xcode5 GM package:
   cp -r ~/Desktop/iPhoneOS6.1.sdk /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/
9. Open Titanium Studio and go to Studio > Preferences > Studio > Platforms > iOS.
10. Hit Refresh and make sure no errors are shown and certificates and provisioning profiles are listed.

Thanks to Tim Poulsen, Eric Merriman and Ayorinde Adesugba for their bits and pieces over the Titan mailinglist.