You need to uninstall the graphical user interface (GUI) on Server1

You have a server named Server1 that runs a full installation of Windows Server 2012.
You need to uninstall the graphical user interface (GUI) on Server1. You must achieve this goal by using the
minimum amount of Administrative effort.
What should you do?

A.
Reinstall Windows Server 2012on the server.

B.
From Server Manager, uninstall the User Interfaces and Infrastructure feature.

C.
From Windows PowerShell, run Uninstall-WindowsFeature PowerShell-ISE.

D.
From Windows PowerShell, run Uninstall-WindowsFeature Desktop-Experience.

Explanation:
A: Not least effort
B: Quick and Easy
C: Uninstalls PS-ISE
D: Doesn’t remove all GUI components

http://www.petri.co.il/switching-gui-server-core-windows-server-2012.htm