Convert Server Core to GUI in 2012

Method 1.

1. Mount the Windows Server 2012 ISO to the host.
2. open an administrative command prompt
3. mkdir c:\mount
4. ‘dism /mount-wim /wimfile:d:\sources\install.wim /index:4 /mountdir:c:\mount /readonly
5. powershell (enter PowerShell prompt)
6. install-windowsfeature server-gui-mgmt-infra,server-gui-shell –restart –source c:\mount\windows\winsxs

Method 2.

The best way is to place W2012 Source file on a share (e.i \\fileserver\W2012Source)
from server core, use net use to map drive to \\fileserver\W2012Source ==> net use \\fileserver\W2012Source /persistent:yes

Then, the command prompt usind DISM to mount W2012 image file from the network drive you just mapped
then launch add-WindowsFeature again and if DISM detect the correct source file you will be able to switch to Core with GUI or Shell GUI

Method 3.

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Dism /get-wiminfo /wimfile:<drive>:\sources\install.wim

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Install-WindowsFeature Server-Gui-Mgmt-Infra,Server-Gui-Shell –Source wim:f:\sources\install.wim:4   (If Drive is f and edition is 4 )