To take care of it, open iTunes, click on the “Store” menu at the top, and choose “Deauthorize This Computer.”
iTunes’ll want to know what Apple ID you’re deauthorizing, so enter that info.
When you’re finished, repeat this process for every Apple ID you’ve authorized on your Mac. That’s all there is to it! But…but…what if you’ve forgotten to do that, and the Mac in question is already gone? You can remove that machine from your authorizations remotely, but unfortunately, there is no way to do one computer at a time—you’ve gotta wipe out all of them and then go back and reauthorize the ones you actually want. Ick.
Keep in mind, too, that you can only deauthorize all of your machines once per year, so don’t go following all these steps just because you’re reading this tip, OK? Save this for when you really need it.
Anyway, here’s how. Open iTunes on your Mac and click on the “iTunes Store” button.
Once you’re there, select the “Account” button on the right and log in.
Assuming that you have more than one computer already authorized, you’ll see a “Deauthorize All” button under the “Computer Authorizations” section on that next page. Unsurprisingly, you can then click that button to revoke permission to play your media from every machine you’ve allowed in the past.
Then all you need to do is go back to each computer you’re currently using, open iTunes, and pick Store> Authorize This Computer to approve it with your Apple ID again. Easy, right? Not at all cumbersome? OK, that’s actually fairly cumbersome. I understand why Apple won’t allow us to deauthorize more often, but that doesn’t mean I’ve gotta like the process.