Can acct be changed without uninstall-reinstall?

I seem to have more NIS accounts than I need, so I will turn off auto-renew on the one that is now superfluous. I have deleted 2 seats (PCs no longer used) from the 3-licesne account to be kept, and I want to transfer one of the now-free seats to another PC (Surface Pro 3) that has a 1-seat-only account/license that I want to discontinue.

Do I have to uninstall NIS from the Surface Pro 3 first, and then re-install from the other account with the now-free seat?  Or, hopefully, is there a way to simply transfer one of the free seats to the other PC?    If yes, what is the procedure?      I hope I've been able to explain clearly what I want to do.

Thanks