I can't see it very clearly on the picture, but under the speaker grill and on the "front" of the speaker grill(front as in side towards the front of the car) near the top there should be some gaps(seperate panels from the doorpocket)... If that's the case: For me, on the(in the pic) bottom left corner there was a screw holding the speaker cover in place(although it looks like mine were bodged in later or something...), so unscrew that, and do a bit of fiddling with a flat screwdriver between the gaps to take the cover off...
If there isn't a screw, but there are gaps: same thing really...
If the gaps aren't there, I suppose you it's one piece with the door pocket on yours, and you'll have to take that off too.. But really, I have no idea wheither you need to take your whole doorcard off or not... Maybe you can just take it off with a flat screwdriver and some bodging, but might damage the doorcard... Anyway, the doorcard is held on click- things, I see you don't have a windowwinder, but if you do: you need to take the windowwinder off by pushing the ring around it...
Why didn't Seat just make all these interiors the same? Would be so much easier!
EDIT: :/ Ok I see I'm slow at typing lol