Remove devices associated with iCloud account
Removing an associated device or computer from an Apple ID
To remove a device or computer from your Apple ID:

Open iTunes.
Sign in to your Apple ID by choosing Store &gt; Sign In from the iTunes menu.
Choose Store &gt; View My Account from the iTunes menu.
From the Account Information screen, click Manage Devices.
Click the Remove button next to the device name you would like to unassociate.

http://support.apple.com/en-us/HT4627