Here's a little tip that I always add to the subject of rear seat removal. For the lower portions of the seat, when pushing back toward the rear of the car, it is possible to overshoot the hole through which the seat frame releases. When that happens, the frame will be held into place in the same fashion as before pushing at all. You'll have the impression that you still need to push harder because the seat won't release upward. Fact is, you can push passed the release hole and the frame will recatch on the opposite side of the opening.
I discovered this when removing my back seats. I was pushing to a point that I thought unreasonable but the seats still wouldn't come out. I pushed with about a 1/4 of the force and they popped right out.
Push just a little and lift toward the ceiling. If it doesn't release, push just a little harder and lift. If you push real hard to start with you might run into the problem described above. It still may take a fair amount of force as already pointed out. My only point really is that it is possible to apply too much backward force. Just something to be aware of.