As with most cars, you can remove the back seat cushion by pushing it back and up. There are two catches; one on each side. Just push back, lift, and it should come undone on each side.
However on this car, you won't be able to actually remove the cushion without first removing both rear arm rests. Easy enough; two screws each. Replacing them is tougher, as it's really hard to get those two screws started. Trick: push the two screws into the arm rest, then stick a small piece of masking tap to each screw from the back, to keep them from falling back out. Then install; it's easy.
Once the cushion is out, remove the bolts and let the two seat backs drop -- then pull them out.