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.