As of the release of Parallels Plesk Panel 7.5 Reloaded and Parallels Plesk Panel 8 for Windows, Parallels Plesk Panel (PP) comes with built-in license management. This is achieved through secure communication with our licensing server through port 5224.
Log in to PP as the administrator and go to the "License Management" option under the "Server" section. From there, select the "Retrieve Keys" option at the top of the PP license key page:
Server -> License Management -> Retrieve Keys
This will retrieve your newly updated license from our licensing server.
Should problems persist, contact support using our online support form.