Windows Server 2012 is the first Microsoft operating system that can change from CLI (Core) to GUI mode. The only way to get a GUI in Server 2008 was to re-install, which is why a lot of system administrators were put off by Server Core. Server 2012 can bounce between the two and it really is quite simple to do. All you will need is the OS disk mounted or inserted into the DVD disk drive.
Let’s pretend that during the Server 2012 installation you selected Server 2012 Core and now have buyers remorse and are ready to wipe your system. Wait!.. you don’t have to re-install!
Simply follow these instructions to install the Server 2012 GUI:
In the Command Prompt launch PowerShell
We need to determine the index number for the server with a GUI from the Operating System image.
Type: Get-WindowsImage -ImagePath path to wim\install.wim
Our index is 2 because the current installed OS is Windows Server 2012 R2 ServerStandardCore
We need to install the GUI features:
Type: Install-WindowsFeature Server-GUI-Shell, Server-GUI-Mgmt-Infra -Source wim: path to wim\install.wim: Index # from previous step
The install will take several minutes. When it’s finished it will prompt for a reboot.
The computer will reboot to the Windows with a GUI.
Please note that there are several ways to do this. However, I found this the simplest.
If you would like to convert from GUI to Core please follow this link: https://crtech.tips/uninstalling-server-2012-gui/