First of all, you need to remove the rear bench seat from the runners





You now need to remove the pins from the rear end of the rails. These will be held in place with a washer, which you can spring off with a screwdriver (or perhaps by hitting the washer end of the pin with a hammer).

Now you should be able to slide the runners of the rails, out of the rear of the van. Make sure you keep the locking mechanism disengaged (by pushing down with a screwdriver) while you remove the rails, otherwise you may scratch the paintwork.

Slide out all 4 runners, making a note of which came from where.

These nylon pieces will probably be broken. The seat will still slide without them, but not as smoothly. It's probably better to chuck the broken ones rather than risk them getting stuck in the rails and jamming the seat.

You now need to reverse all the steps above to refit the seats.The two runners that held the middle bench should be swopped over and rotated 180 degrees before replacing them. This will allow the middle bench seat to be rotated when you refit it.
When you return the pins to the end of the rails, it's not necessary to fit the retaining washer. I didn't bother and the pins haven't come unseated in two years.