The bottom part is really easy. There's 2 pushbutton release about 5 inches from each end along the bottom of the lower seat cushion where mounts to the car. I had run a flat blad screwdriver across until I hit the side of the release and then moved it to the front and pushed the release button. Do the same to the other side and the whole bottom will come right out. I'm not sure about the back rest, but it doesn't look too difficult.
I broke mine while taking them out but it doesn't matter since she will never see them again anyway and there is no possible way for them to fit in the car either.