If you are being told that the catalog needs to be upgraded, that would indicate that you were running an older version previously. Upgrading a catalog is really a seamless operation. Simply agree or allow Lightroom to do the upgrade. That's all there is to it. The upgrade process will create a new copy all your catalog, leaving the old version completely intact. Once the conversion or upgrade is complete Lightroom will start and the program will continue right where you left off previously. The new catalog will have the same name as the old one, except it will have a -10 added to its name. That's all there is to it, nothing to worry about really.
Incidentally, I use Lightroom Classic on a Windows 10 PC.