Before Plesk 12 you could upgrade your old licenses to the latest version without trouble. Upgrading from Plesk 9 to Plesk 10+ is no problem and this can be done by simply contacting our support department.
Upgrading to Plesk 12 is unfortunately not possible from any of the previous Plesk versions. The license structure is so different from the previous versions that they do not translate well.
To get a Plesk 12 License as a replacement for your current, you will need to order a new license and delete the old one.