First, you have to get vernier calipers so you can take precise measurements. I have mechanical ones for both metric and inch scales, but you can get a cheap electric one that does both. Your hoe cyls will be metric, most likely.
Removing and measuring your seals is the next step. Note the shapes and configuration. As a minimum, you need to replace the rod-wiper, the rod seal inside the gland, and the main piston seal(s). You usually do not need to replace the rub-rings or the O-rings not subject to any wear, but do so if they are in a packaged kit or look questionable.
I like to measure the slots where the seals go, rather than the seals themselves. Sometimes there are backing ring(s) that make up 2 or 3 parts of a single seal. You will probably need a U-cup seal for the gland, and a sliding seal for the piston.
I know it seems daunting the first time, but I figured it out without help, and before there were any online videos to watch.
There is a Special Tool you should get to put in the gland seal, but it is not expensive.
There are many many Utube vids now to give you guidance. Here is an engineer's perspective on how the seals work if you want to go a little deeper: