I've got a full sized JCB so I presume you have a full sized one also.
From what I understand, if I wanted to remove the main cylinder on my BH, I 'd have a problem because the cylinder is longer than the hole is. The way around this (in my case) is to dig a hole where you can "bury" the backhoe arm and by doing so, in my case, give your self access to the cylinder and remove it.
I've never done this but on my machine, I can see how that would be necessary. The cylinder in my case, is INSIDE the boom arm and not external like I've seen on some machines. The hole for insertion is near the pivot pin so once you imagine the hoe buried and extended into the ground it's easy to see how it works.
I DID once take the dipperstick cylinder off (single handedly), had it repacked and reinstalled it (alone)
I do NOT recommend anyone try that with these things. now that I know what I know regarding the stupid "little" dipperstick cylinder, I'd have to be a nutcase to try lifting the main cylinder alone.
Hopefully this will work for you or if not, you'll find an easier way.