If you want to move, save the new runtime first (copy it to another place), then copy the old runtime over, then copy the new one back over the old one. That way you are sure you keep all files the new Poser version needs: All Poser configuration files are inside the runtime, Poser would be quite annoyed not being able to understand them anymore.

Needless to say, before doing this, back up both runtimes. Anyway, back up your runtimes often...