How to Disassociate an iPhone From a Computerby Tyson Cliffton
Apple makes it possible to associate your iPhone with up to 10 computers or devices. Each computer associated with your device can access content you've previously purchased from the iTunes Store, such as apps or music. Associating your iPhone with a specific computer also lets you download operating system updates for your iPhone on that computer. However, you can always disassociate your iPhone from a specific computer through iTunes using your Apple ID.
Open iTunes on the computer you want to disassociate with your iPhone.
Click "Store" and then click "Sign In." Enter the Apple ID and password associated with the iTunes account you use with your iPhone. Click "Sign In."
Click "Store" and then "View My Account." A dialog box appears, prompting you to enter the password associated with your Apple ID.
Enter the password associated with your Apple ID and then click "View Account" to open the Account Information screen.
Click "Manage Devices." A list of computers associated with your iPhone appears.
Click "Remove" to the right of the name of the computer you want to disassociate from your iPhone. The devices are disassociated from each other immediately.