All you have to do to remove the bottom part is pull up on it.
The best way that I can describe how the bottom is fastened in is by saying that it is being held down by two metal hooks that snap into the car. Each hook is located toward the front of the cushion on each side where a person would sit. I would recommend pulling up on one side at a time.
It takes a lot of force to pull the hooks out of their fasteners, so don't worry about breaking something when you are pulling up on the cushion. It's normal to have to pull on them very hard to get them to come loose.
I'm not 100% sure, but if I think that the bottom portion of the rear seat will not come out with out unbolting the center hinge for the back portion. fold down the rear seats and lift the carpet backing up a little to examine the hinge. If I remember correctly, there is a foam coated wire "loop" that is built into the bottom portion of the rear seats, and the hinge for the seat backs goes through the center of the loop.
Man, that all sounded like it could have been pretty confusing.
If you get stuck/confused/or just need some extra help, let me know.