To uninstall newer versions of Xcode is much like deleting any other app from the Mac:
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Next you’ll probably want to delete the user Developer tools folder, found at the following location – note this includes user developer data, so don’t do this if you have projects and other data in Xcode that you haven’t backed up elsewhere or you otherwise care about:
The directory is ~/Library/Developer/, the user folder should contain “Xcode” and “CoreSimulator” folders:
Uninstall Xcode 7
This will remove everything pertaining to Xcode from a Mac:
sudo /Developer/Library/uninstall-devtools --mode=all
Don’t Forget to Delete the Install Xcode Application
If you uninstall Xcode, the original Install Xcode application is probably still sitting in your /Applications/ folder as downloaded from the Mac App Store, don’t forget to delete this too otherwise you are wasting 1.8GB of disk space.