Btw, it isn't really clear what do you want to do?
1. Is the account currently logged is attached to a facebook account?
2. If the account is not attached to any facebook account, is it your account or somebody else?
3. What specifically you want with the account currently logged in? Get rid of it?
4. What device are you using?
If you are logged in thru facebook, check the SETTING icon at the right bottom of the screen (looks like a gear). Tap the icon and on the SETTING screen, tap the LOGOUT BUTTON beside the facebook text description.
If not:
Just restart (turn it off and turn it on) your device. When you open the apps, At the main screen it will ask you to logged in using your facebook account or play with the current user.