I'm pretty sure this is not possible but just wanted to check. Windows Server 2012 R2 is basically a totally separate release right? I can't update R1 to R2 via Windows Update can I?
I can't update R1 to R2 via Windows Update can I?
No. No, you can't.
Also, it's not named Windows Server 2012 R1, it's just Windows Server 2012.