Activating a Windows Server 2012 R2 Evaluation Installation With a Valid License

I was trying to activate a Windows Server 2012 R2 server that I installed as an evaluation.
However when I entered the license key I was getting an error message.

"That key can be used to activate this edition of Windows. Please try a different key"

So after doing some digging on the internet I found the following command to remove the existing
key and add a new key.

To remove the current key I ran,

slmgr -upk

To install the new key I ran the following command with the new key,

slmgr -ipk XXXX-XXXX-XXXX-XXXX 

However I got a wired error and it failed.

“Error: 0xC004F069 On a computer running Microsoft Windows non-core edition, run ‘slui.exe 0x2a 0xC004F069′ to display the error text”

So after doing more digging on the internet I found some more information.

found the DISM TechNet reference and the DISM.exe /Online /Get-TargetEditions command. It seems like I need to change the Windows edition when activating. So I had to customise the command as below and ran it again (I'm activating Windows Server 2012 R2 Standard Edition).

DISM /online /Set-Edition:ServerStandard /ProductKey:XXXXX-XXXXX-XXXXX-XXXXX-XXXXX /AcceptEula

and WooHoo! it worked! Server needs a reboot once you run this command though.