Change from RHEL Desktop to RHEL.

Hi rhn-users,

Back in March '08, I renewed all of my Red Hat entitlements with a VAR
that Red Hat hooked me up with. I changed all the entitlements to be
co-termed ending in 2010. I also upgraded a few RHEL Desktop
entitlements to RHEL Basic Server. 

How do I change the RHEL Desktop machines to RHEL Basic Server? Can I
even do this? Do I have to reinstall the OS?

Thanks for any help,

-Allen