When Server Core originally shipped, a lot of Windows admins avoided it because you could only use the command line, but this changes with Windows Server 2012 which enabled the use of a hybrid mode.
Step 1: Go into Server Manager > Manage > Remove Roles and Features
Step 2: Pick the server you want to remove the feature from:
Step 4: Click on “Remove Features”
Step 6: Once the server is rebooted and you log into it, you are finally in Core. Congrats!