How can i remove the back seat of a 2001 buick lesabre to change the battery?

The bottom cushion hinges forward on hooked anchor tabs at the lower front of the cushion. Take hold of the bottom cushion at the seam where it meets the bottom of the backrest and lift. The bottom cushion will hinge forward and the hooked tabs at the lower front of the cushion will release from the anchors so that you can lift the cushion out of the car.