From what I have seen an Uninstall/Reinstall is the best way to proceed.
Is your licence for Lr a perpetual one?
If you are asking me is it in the Cloud no it isn't
I asked because an awful lot of people have recently been confused between downloading the Cloud and the perpetual versions of Lr - although I'm not automatically assuming your'e guilty of this - and can't understand why their serial no won't unlock their new software.
If the wrong version has been installed, then it must be uninstalled and the right one downloaded.