How to know if eligible for Mac upgrade

Hi,
New to Parallels because I am taking over supporting a help desk and this company seems to have about half a dozen people using Parallels to jump to their virtual Windows VDI. How do I know if anyone is eligible for a free upgrade to the software? For one user, the version is 19.3.24519. Do I jump on their Mac and try to find a license key (if so, where would that be found). Then once I have a key, how do I find the upgrade?

I am asking this as a couple of them are experiencing the odd problem and so I want to see if a new version has addressed that problem.

Thanks,
Albert