32 bit RDP clients store their license under the key HKEY_LOCAL_MACHINESoftwareMicrosoftMSLicensing.

Warning If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.

To clean the client’s license cache, just delete this key and its subkeys. The next time the client connects to the server, it will obtain another license.