I've been dying to "tweek" the padding on the backrest.
Position seat up at rear and all the way forward.
Pull out from the bottom about 1 inch or so
Insert screwdriver pushing upward to unhook the 2 plastic tabs (1 side @ a time)
Swing out the bottom and pull down to remove.
I added closed cell foam (about 3/4inch thick) just below the phoney lumbar mechanism.
HUGH IMPROVEMENT in about 5 minutes time.