Yes, if you'd like to change the account used for the Kindle or give the Kindle to another user, you'll first have to deregister the Kindle from the current account.
To deregister your Kindle:
1. From the Home screen, tap the Menu icon, and then tap Settings.
2. Tap My Account and then tap Deregister.
3. Tap Deregister again to confirm.
You can also deregister your registered Fire tablets, Kindle e-readers, or Kindle reading apps online from Manage Your Content and Devices : www.amazon.com/mycd"