I have to use Xcode occasionally, and have now come across a problem where I've upgraded to Xcode 4.6, but another piece of software I'm using doesn't support it, so I need to go back to Xcode 4.5.
I'm not used to the way Macs work in general, so if the answers provided could be written with that in mind, that'd be helpful. :)
I'm assuming you are having at least OSX 10.7, so go ahead into the applications folder (Click on Finder icon > On the Sidebar, you'll find "Applications", click on it ), delete the "Xcode" icon. That will remove Xcode from your system completely. Restart your mac.
Now go to https://developer.apple.com/download/more/ and download an older version of Xcode, as needed and install. You need an Apple ID to login to that portal.
When you log in to your developer account, you can find a link at the bottom of the download section for Xcode that says "Looking for an older version of Xcode?". In there you can find download links to older versions of Xcode and other developer tools
来源：https://stackoverflow.com/questions/14756026/how-to-downgrade-xcode-to-previous-version