While on travel, I rented an Amazon Prime movie in a hotel room; and since returning home it dawned on me, I never logged out.
To Logout: You will log into your Amazon Account locate the device and deregister it!
From the Amazon website, go to Your devices.
Login with your Amazon account credentials.
Click Deregister. Your Device will be deregistered from your Amazon account. This will remove all content from the device and many features will not work. Items you purchased from an Amazon store will remain available in the Cloud and can be downloaded again. After deregistering, you can register your Device to another Amazon account.