Don't rush. Take your time. I had to hang the car in the overhead and come out through the escape hatch. Then do the whole thing off a ladder with my helper working the chain falls on the car top.

A guy in here, Montana, lined it out pretty good.

"If your jack heads are accessible with the car on the buffers:
1. Place diapers around the base of your jack
2. Mount a picking plate at the top of your rail
3. Hang chainfall off of the picking plate, center of jack
4. Run down, pull 1" bolt, manual lower to buffer out, LOTO, close MR oil line valve
5. Pull hat off of the jack, open bleeder to verify you're down
6. Use strap wrench to remove top head, set aside
7. Screw in 1" eye bolt and hoist small piston out, lower down and set on pit floor
8. Screw top head back onto large piston
9. Use strap wrench to remove bottom head
10. Choke large piston under the top head and begin hoisting
11. Use a small oil pump to pump the oil into a bucket as you hoist the large piston out.
12. Remove four 1/2" bolts from the bottom retaining plate
13. Pull the check valve hard to get it out and remove the old o-ring from the inside groove.
14. Replace the internal seal
15. Install the new check valve o-ring into the groove and shove the new check valve into it
16. Reinstall plate and bolts
17. Lower large piston back into jack casing
18. Remove top head and set aside
19. Remove bottom head and replace o-ring, wear strip, and seal (use tool that covers threads)
20. Slide bottom head back on (use cone tool that goes onto the top of the piston) and screw back on.
21. Lower small into large piston
22. Rebuild top head just like the bottom head and install
23. Put everything back together and bleed air

I'm sure I've missed a bunch of steps because of my ADHD, LOL, but you get the just of it. The last car I did I had to poke the car and work under it because the jacks were real short and the heads could not be accessed with the car on the buffers. I did not like that repair. As I get older I don't like being under poked cars. There are definitely a few ways to do it. Hopefully some other mechanics will give some more good tips. I hope this helps you a little bit. Just take it slow and think through it. You'll probably make a couple mistakes but that's ok, you'll learn how to do it."