There is no real need to do anything until analogue is switched off, although you can act in advance if you prefer.
When analogue is switched off your VHS video recorder won’t be able to receive any programmes by itself. However, if you are really happy with it then you could buy a set-top box (either for aerial or satellite reception) and simply use it to supply programmes to the video recorder.
So you would have two set-top boxes, one to record from and one to supply programmes to the TV set. In any case, your old video will always play back your tapes quite independently of the TV broadcasts. So even after analogue is switched off you will always be able to play your tapes as long as your video recorder is in working order.
If your video recorder is getting a bit old though, it might be as well to buy a new digital recorder. This will need to be the type that works from either an aerial or from satellite, depending on which you have.
The modern digital recorders are very easy to use, and if you have always found the old video a bit confusing you’ll get a nice surprise if you get a new digital one.