In 10.10 you should use (Assuming you've installed few versions of Xcode as Xcode6.1, Xcode6.2 and Xcode6.3, and want to make Xcode6.3 as default one).
If you do a lot of work in both the current and beta version of Xcode run sudo xcode-select --switch /Applications/Xcode.app to select the default xcode and rename the beta Xcode to XcodeBeta.app or Xcode10.app.
Whenever you want to upgrade just rename the Xcode and restart terminal.