I swapped the leather from one seat onto another the other weekend. It's not too bad a job - you just need to look to see where the different parts clip/fix in and remove them. I thought about doing a how-to, but was pushed for time!
It went something like this:
Undo the plastic adjuster cover.
Unclip the bit you sit on front and rear, then lift off. Might be lightly glued.
Side bolsters are held on with wire that runs along their length, clipped under metal tabs. Remove those.
Back-support is clipped underneath, glued lightly to the frame, and more of the wire/clips at the top.
Once the back support's removed, you can get at spring clip things that hold the headrest in. Remove that.
Undo the screw under the flip-forward handle to loosen the plastic trim. I couldn't figure out how to remove it, but the leather will slip past it.
Refitting is reverse of removal. I used a bit of impact adhesive to stick the back and bottom down.
When I was done, I had a lovely new seat, and some very trendy leather kneeling mats