Edit: I called Head Office (the Claremont number) and the consultant noted I am a legacy Vitality member (pre-2010) and she advised the easiest and most cost effective method for me is going to be to club change, so I have to:
1) Call them them at Head Office the day before I want to change over, then they will action it
2) Pay R50 at reception at the club I'm going to (the system will note that I need to pay this)
3) When I want to change back call them again at HO to action the change
4) Pay R50 at reception at the club I'm returning to
Going the Premier membership route involves a R297 monthly fee, and then a R200 admin fee to downgrade again.