In FamilySearch Central the first row under "Task to Do" is the logout link. As soon as you log out it will let you log back in again as a different person.
On the FamilySearch Login screen, that will appear, you can make adjustments to your settings for your login to be remembered/or not, by adding or removing the below check-marks.
- Remember my sign in and password
- Automatically log in (bypass this screen)
You would need to at least login once with the new settings for it to be remembered later.