Q: My iTunes account says that I have 4 devices, when I really just have one. How do I delete the other 3 so that I only have one registered for my account?
A: The three other devices may represent a computer or computers that you previously owned, or it may simply be that you have reinstalled your operating system or performed a significant hardware upgrade on your computer without deauthorizing it first. iTunes uses aspects of your computer’s hardware configuration and operating system to uniquely identify your computer, so any significant changes to either will cause iTunes to assume that you are authorizing a different computer. For this reason, you should always deauthorize your computer before reinstalling the operating system, performing major hardware upgrades, or sending it in for service.
There is no way to remove a specific authorization if the computer or configuration that it is assigned to is no longer accessible. iTunes does allow you to reset ALL of your authorizations once per year, but only once you have reached the five computer limit—at that point a “Deauthorize All” button will appear on your iTunes Store account page beside the number of authorizations. Until then, however, you still have an empty authorization ‘slot’ remaining, so there’s no need to be particularly concerned about removing the other three phantom authorizations.