The upgrade path was simple. I just needed to take one exam "Upgrading your skills to MCSA Windows Server 2012" 70-417
Well, for the first time in my IT career, I failed the exam!
The 70-417 exam is split into three mini exams, each with a pass score of 700. There is the 70-410 (Install and Configure), the 70-411 (Administering) and the 70-412 (Advanced). If you fail one of the these you fail the whole exam. (i.e, if you scored 990 in exam 1, 1000 in exam 2 and 690 in exam 3, you would fail the whole exam with your lowest score, 690).
Of course, the exam focuses a lot on the new features avaliable in Server 2012, but it also tests your knowledge gained from Server 2008 certification paths on topics that haven't changed much since so aren't repeated in the MCSA 2012 learning material (for example, DNS Zones, Certificate Services, AD Forest and Domain Trusts etc)
I'd recommend brushing up on ADFS, NAP, IPAM and Dynamic Access Control especially if you've never used these before.
Fortunatley, I have a free retake using the 'Second Shot' offer. Hopefully better news next time.
Resources used so far
"Upgrading your skills to MCSA Windows Server 2012" ebook by JC Macklin
"Upgrading skills to Server 2012 Jump Start" Microsoft Virtual Academy
Test lab setup on my laptop with a few virtual machines (Domain Controller, File Server, Server Core) and a Misc Server (for playing around with roles such as RDS, IPAM, NAP)