In this mini how-to we show you how.
You will be prompted to slide in your account credentials, then Deauthorize it.
Deauthorize All ComputersNote: it’s possible for you to only use the Deauthorize All Computers once per year.
Go into the iTunes Store and sign in if your not already.
press the Account button on the right side of the main page.
Enter in your account credentials again and click Account Info.
On your Account Info page tap on Deauthorize All.
Click Deauthorize all computers at the confirmation screen… You will then get a message that you have authorized one out of five available…click OK.