There is no easy way aside a file copy and paste to move virtual machines between 2008 R2 and Hyper-V 2012 R2 with the native tools. You can move from 2008 R2 to 2012, but not to 2012 R2.
I have found the easiest, quickest way to do this is to use the VEEAM hyper-v backup/restore utility. It requires a agent on the servers you are moving VM’s from and to and seems to work very very well, quick also with up to 1.7 compression and a good backup on the host you use for the transfer. Veeam Backup/Recovery
When you restore your 2008 R2 VM it updates the WMI, adds it to the cluster (if you want that) and brings it back online.
Well worth a look if you want a painless migration.
