I'm currently running MacOS Mojave/Parallels 13.3.2. For various reasons, I can only upgrade to Catalina, not to more recent versions of the OS. Therefore, for compatibility, it seems I need to upgrade to Parallels 15, since more recent versions of Parallels are not compatible with Catalina. I see that I can download the Parallels 15 .dmg file from the Parallels website. My question is, how do I purchase and obtain an upgrade license for Parallels 15 in order to activate it?