How To Log Out Of the Joomla 3.X Admin Control Panel?
After logging in to the Joomla 3.X Admin Control Panel, locate the Super User, drop down list box at the extreme top right hand side of the Joomla Admin Control Panel as shown in diagram 1.
Click the Drop Down list box labeled Super User.
From the choices displayed select Logout, to logout of the Joomla Admin Control Panel.
NOTE: It’s always good practice to Logout of the Joomla Admin Control Panel when you’ve finished working with it, rather than just closing the Browser window while still being logged in.
When successfully logged out the Joomla Admin Control Panel, the Joomla Login screen is displayed immediately in the Browser as shown in diagram 2.