How to Remove an iTunes Authorization
Authorizing a computer in iTunes allows you to sync your purchases from that iTunes account onto that computer. You may only authorize up to five computers per account. If you wish to authorize another computer after you reach this limit, you must deauthorize one of the existing computers first. Apple also advises deauthorizing your computer before you dispose of it in any way, whether you recycle it or sell it.
Instructions
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1
Open iTunes. Click "Store" at the top of the screen to open a list of options.
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2
Click "Deauthorize This Computer" from the list of options that appears.
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3
Enter your Apple ID and/or password in the appropriate fields of the new window that opens.
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4
Click the blue-rimmed "Deauthorize" button in this window. This deauthorizes the computer you are currently using.