I've replaced several. Depending on how the cylinder is assembled it can be relatively easy or very hard. The worst are cylinders that the end screws on. Always a hassle getting them apart.
Once you start disassembly just be conscious of how everything is assembled. I stack pieces as they come off. If I'm worried about it I'll sometimes use my cell phone to take pics of the various seals and the gland before I remove the seals and O-rings. Pay particular attention to the pieces that are not uniform. For example you might find an 0-ring that is round on one face and square on the other. Or you may find an 0-ring with a plastic washer on one side of it. That's where the pictures come in, so you don't assemble it with the washer on the wrong side.
Look at is as adventure!!!! If you can't make yourself tackle it drive over to the nearest equipment dealership and ask the shop foreman what he charges to rebuild your cylinder. After you pick your jaw up off the floor you will have the motivation to do it yourself.