By now, you know most of the Hyper-V features that Windows Server 2012 and Windows Server 2012 R2 bring to the table. If you already have an older Hyper-V setup in your data center, then you should definitely plan to upgrade to Windows Server 2012 R2. However, for this, there are always two opinions. The first is to follow the in-place upgrade options as per the MS guidelines. The other is to migrate to the newer platform. Both the options have their pros and cons and experienced consultants recommend that you opt for migration rather than in-place upgrades. However, with some key features removed permanently from Windows Server 2012 R2, which were deprecated but still existed until Windows Server 2012, migration to the former is not a straightforward option anymore for older platforms.

The following links give you important information about upgrading to Windows Server 2012 R2 and migrating server roles to the same platform:

Windows Server Installation, Upgrade, and...