Resetting the iTunes Authorization Counter
Q. I am getting messages from iTunes that say I have already authorized the five computers I am allowed to use with my iTunes Store purchases, but I no longer own three of those five machines. Is there a way to un-register them from my iTunes account?
A. You can de-authorize the computers you no longer own in your iTunes Store settings, but in doing so, you must de-authorize all your computers associated with your account. Once you de-authorize all the Macs and PCs you have used to play your iTunes Store content, you can go back to each computer you currently own and authorize them again.
To get to your iTunes Store account settings, open iTunes, go to the Store menu and choose View Account; you can also log in by clicking on your name or profile icon on the right side of the iTunes window and selecting Account Info. Log in with the Apple ID you use to buy iTunes Store content.
When you arrive on the Account Information screen, go to the last line of the Apple ID Summary section, called Computer Authorizations. Click the De-authorize All button to reset your number of authorized machines to zero. (Keep in mind that de-authorizing the computers does not remove the iTunes content from each one but merely denies the machine the permission to play the music and videos.) You can only de-authorize all your computers once a year.
Now that you have removed all the computers from your iTunes Store account, you can add each one back. Open the iTunes program on each Mac or PC, go to the Store menu and choose Authorize This Computer; if you do not see the Store menu in the Windows version of iTunes, press the Control and B keys on the keyboard to reveal it.