There is few method to logoff from the Window 2012. Please refer as below
Method A: Normal Way
(1) Move your mouse over the upper right corner (1st red box)
(2) It will come out 3 button as 2nd red box
The upper button, Search button.
The middle button, Start Menu.
The lower button, Settings button.
(3) Click on the Setting button.
(4) Click on the Power Button
(5) Select Disconnect
Method B: Alternative way
Open task manager and disconnect under USER tab
Method C: Faster Way
(1) Open PowerShell window
(2) Just type in
So, just choose the method you prefer.