I have a development machine that another employee (who has left) purchased Xcode on. Now I want to update Xcode, but I don't have that employee's apple ID information. I signed out of the App Store and back in with my account, but it won't let me update or re-buy the app because it was originally bought with his account. Any ideas?
Simply delete the app from your machine. The store prevents two copies of the same app from being installed as a general case
You should then be able to re-buy it as it would be a fresh download - signed for the account you prefer rather than a re-download of the app signed for the old Apple ID.