To convert the GUI version of Windows Server 2012 to Server Core:
- In Server Manager, select Manage > Remove Roles or Features
- If the Before You Begin page appears, select Next
- At Server Selection, select the server you want to convert to Server Core and select Next
- At Server Roles, no changes are needed. Select Next.
- At Features, expand User Interfaces and Infrastructure, remove the check from Graphical Management Tools and Infrastructure.
- In the Remove Roles and Features Wizard pop-up box, select Remove Feature
- Select Next
- At Confirmation, select Remove
- Once completed, select Close
- The computer will need to be restarted to complete the changes. Type shutdown /r /t 0 and press enter to reboot the machine immediately.
Once restarted, you will be in the Server Core interface.