I general, if you can leave the cyl base end secure, and remove the rod end bolt/pin. Spin the cap off the rod end and pull the assembly out of the cyl bore. Have a pan or catch basin handy to catch any spills. After the rod and piston assembly are out, clean off everything with a lint free rag, and lay on a clean work area. Observe what parts go where, and use a soft pic to remove the 0-rings and seals. remove the piston, might be tight, as it was installed with Loctite. Soak the o-rings in hyd fluid and install observing any directional seals. Install the rod upper seals first, and then install the piston with some Loctite. I think red. Install the piston seals, and then lube everything with hyd fluid and re-install. You can fill the cyl with fluid if possible, and if not, the cyl will auto bleed the air as you cycle the cyl several times.
Some people use warm to hot water to soak the o-rings, if they are difficult to install.
You could make yourself a spanner wench to fit those holes, or just tap the holes with a blunt rod and hammer until loose.