Which license limit? What exactly are you trying to accomplish?
Which OS and SP are you running?
If your problem is that a lot of TS CALs are permanently issued to
clients that since have been discarded (which happens if your TS
CALs were installed before you installed SP3), then you should
install SP3 (or at least the Licensing Enhancements) and then call
the Clearinghouse to get those licenses re-issued.
TS CALs installed after SP3 have an expiration date. Those
licenses will automatically be returned to the pool on the License
Server after 51-89 days. New clients get a temporary license in
the meantime.
If this doesn't cover your problem, feel free to repost with more
details.
287687 - Terminal Services Licensing Enhancements
http://support.microsoft.com/?kbid=287687