You can only have 5 computers authorized to listen to your purchased music at a time in iTunes. Eventually, you might have to deauthorize one or more of them so that you can add another computer. Unfortunately, Apple doesn’t give you a way to manage which computers to keep authorized once the computer doesn’t exist anymore. You have to deauthorize them all at once and then manually reauthorize them one by one.

Here’s how you deauthorize all of your computers in iTunes.

1. Open iTunes and enter the Music Store.

2. Click on the button in the right corner. This should have your email address on it.

3. Type in your username and password and click OK.

4. Click Deauthorize all.

5. Click Deauthorize all computers.

Now you can reauthorize the computers you wish to use one by one by selecting Store and Authorize Computer.