Gently push up the front of the seat cushion to find a metal snap or hook. Pull or slide the cushion to release it from the snap or hook.
Swivel the chair so you can access the side. Reach between the armrest and the cushion side for another hook or snap to release. Repeat on the other side.
Swivel the chair around so you can access the back of the seat cushion and lift it up. You will see a hook just as the one in front. Pull the cushion up and back to release it from this hook.
Pull on the front of the seat cushion to slide it from the chair.