Updates to the virtual machines are typically performed as in the physical environment. For Red Hat virtual machines updates can be downloaded from the Red Hat Network. For Windows virtual machines you would apply the relevant MS update mechanisms. There is no specific integrated function in RHEV-M to update virtual machines or templates.

Centralized patching mechanism for Red Hat machines is possible via Satellite. RHEV also shows errata information on updates for RHEL hosts and guests OS.
This is a Fee-based Add-On; Details - http://www.redhat.com/en/technologies/linux-platforms/satellite