To remove door cover one gets brave.....
1) Prise carefully the black cover on the side of the window switches, it will eventually come off, remove screw hidden deep at the end nearest the lock, with some wriggling the whole switch unit will come off (cannot remember if there is another screw....). Unplug cable from switch.
2) Remove speaker cover - prise off carefully. Remove speaker (4 screws and unplug cable) and
store carefully
3) Remove fabric trim by carefully easing from backing
4) Should now be able to see some of the mechanism. Reconnect window switch and
lower window about 5cm - assuming it can still be moved.... 2 bolts on the slides should come into view. Tape up the glass to the window frame to hold in position. Loosen these two bolts - they fix the regulator to the glass. Once loose then drop mechanism clear of the glass. Disconnect switch again.
5) Now undo remaining screws to remove the moulded inner part of the door that the regulator is fixed to. 2 screws at the bottom - loosen a long way, no need to remove (yet), and an assortment of other screws that are (fairly) obvious. Now comes the fun bit - on my door anyway - the door lock area. There is a white plastic bit that is fixed to the moulding and the door lock. Now I couldn't see
how to remove this and so drilled out the obvious plastic moulding plugs that held them together and used a bolt in re-fitting - must be a way otherwise though
6) Carefully disconnect door pull cable at the inner handle end, small clip.
7) Remove (ping!!) the black cover that hides the mirror connector and disconnect mirror cables
8) Lift moulded unit upwards and then outwards to reveal (knackered) regulator. Fixing is obvious, but ensure electrical cables go back the right way to prevent fouling the mechanism. Assuming you have the SEAT unit, then swap them over (easy and obvious) and in the great Haynes manual tradition replacement is the reverse of removal.....
9) Also have jump leads handy.....ignition needs to be on to move windows up and down, radio is on for company, the windows are moved a few times, the ignition gets left on, the interior light is on and the battery is a few years old and the wife is not happy......
Have some pictures to hand (will try to attach in due course) and with some web trawling there are also some guides out there. Would be able to do it in under an hour with a little more practice - allow a long afternoon the first time!! Enjoy.....