We're getting really close to shipping Hyper-V. Today, we can announce that RC1 is available.

If you're already running RC0, the upgrade is really simple. Unlike the Beta to RC0 update, virtual network configurations and virtual machine configurations are now compatible and are migrated in-place. The only gotcha to watch out for is that saved states are not compatible, which includes online snapshots. So please make sure online snapshots are deleted and merged, and your virtual machines are shutdown cleanly before applying the update.

If you are still running Hyper-V Beta, take a look at KB949222 for more information. Although that KB was written specifically for Beta to RC0 updates, the same overall information applies for Beta to RC1.

Link: John Howard's Blog