remove the hidden retaining clip from the pivot cover (push it through with a small screwdriver/punch/dofer), it can be picked out after the cover is removed (shown sticking out of the cover ready for refitting)
remove the pivot bolt (15mm socket) and the spring clip on the tensioning pin.
On the other side prise off the adjusting knob, draw out the shaft. Unscrew trim retaining pin and repeat to remove the back rest from the seat section.
Unclip the seat cushion, this is a length of plastic at the back and all around the bottom edge a strip of cardboard stuck onto the cloth to form a clean edge to teh seat.
Take the foam cushion off, you are again faced with 14 of 18 wire rings to remove.
You do not need to remove all 18 of the clips as the heater pad is shaped and can be fed over the cloth cover if you leave 4 wire rings still attached.
Once again carefully strip the heater pad from the cushion
wire conections to the pad
Refitting will be a job requiring patience