Use the Deauthorize all option and then reauthorize any computers that you still have and want to use. This only affects computers, not iPhones or iPads.
See the following instructions from Authorize or deauthorize your computer for iTunes Store purchases - Apple Support
If you need to deauthorize a computer that you don't have access to
To deauthorize a computer that you don't have access to, you have to deauthorize all of your computers. Then authorize each computer that you have again. You can deauthorize all computers only once a year.
- Open iTunes.
- Choose Account > View My Account.
- Sign in with your Apple ID and password. Forgot your Apple ID?
- At the top of your Account Information page, go to the Apple ID Summary section.
- Next to Computer Authorizations, click Deauthorize All.
- Authorize each computer that you use again.