Each window has 2 fold-over clips which attach to the regulator. Release the clip by lifting it, and then slide the clip and the fibre washers off of the regulator.
It might be easier to point you towards the manual.
Take note that R&R'ing the fixed plate glass in the rear doors is quite an ordeal, and the book shows you the only way to do it without breaking things.
http://www.k-jet.org/files/greenbooks/700/TP31127-1_700_body_fittings_incomplete.pdf
This PDF copy from K-jet.org isn't complete, but IIRC it has the procedure in it. (Been a while since I looked at that file because I picked up a complete hard copy of that green book).
If not, please reply in this thread and I'll scan the pages you'll need from my hard copy.