Block the rear and jack up the front.
Disconnect current lines to bags.
Puncture the existing bag so that air can escape. You can even cut it up between the springs.
Use a large flathead screw driver and a large vice grip to rip out the bottom disc under the bag (through the hold where the lines plug in.
Grab and rip out the bag (through that same small hole!) by twisting, grunting (bad words begin to form in your head)
Remove the top disc by pulling it through the springs.
Flatten and roll up the new air bag. Then close it to create a vacuum. Roll it flat again.
Cram the new bag up into the small hole by twisting the bag. You can cover with soapy water to assist. (even worse words continue to form in your head regarding the designer of this process)
Slip the top disc in
Slip the bottom disc in.
Hook up the hoses.
Fill with air to 55 psi.
It's common to lose 5 psi (I did) so the next day, you need to add another 5 psi to bring them up to 55 psi.
Air Lift instructions are pretty good.