Turn the chair upside down and lean it against a wall or desk if you can. Otherwise, turn the chair on its side so you can easily access the seat and see where it attaches to the chair frame.
Remove the bolts, screws and clips that hold the seat in place. Each chair manufacturer uses different fasteners to hold the chair seat to the frame.
Set the bolts, screws and clips you remove aside. Keep them in a coffee can or cup so they do not get lost.
Remove the seat from the chair assembly and set it aside. Watch for loose parts that may fall out of the space between the seat and the frame. Set those parts aside with the others.
Fasten a pipe wrench on the main cylinder of the pneumatic office chair. Turn the wrench to loosen the cylinder and allow you to remove the gas cylinder that allows the chair to move up and down.