Expanding the C: Partition for a Direct-Attached LUN

Microsoft Windows has a way of filling up the C:\ partition, but few native tools to deal with a full volume. I have a Server 2008r2 machine with a 36GB volume directly attached to a RHEV VM via my RHEV cluster nodes. I have expanded this volume, via my Storage Area Network, to 50GB. However, the RHEV manager indicates that this volume is still at 36GB. What do I need to do to get RHEV to see the additional disc?

I have tried shutting down my VM, deactivating the LUN, and reactivating it, to no avail. The RHEV manager still sees only 36GB, and so the VM's host OS only sees 36GB. If is saw 50GB, I would be easily able to expand into it.

So, what do I need to do to get RHEV to see the additional disc?