Did you find an o-ring leaking? No reason to change them unless they are leaking, you run more of a risk of making them leak by taking them out and putting them back in.
You unplug the injectors, move any wiring out of the way you need, undo that big bolt/stud on the top of the blower, and the 4 10mm nuts(back right is a nut/stud) and lift the rail up. There's no need to disconnect the fuel lines from the rail, unless you want to. Pop the clips off that hold the injectors on with a straight-slot screwdriver. When you pull an injector off, there will be fuel that comes out, so be prepared with a bunch of rags/towels.
Swapping the top o-rings is easy mode. Just use a pick to roll them over the lip. (Can probably use your fingers if they are old and worn)
Swapping the bottom o-rings is trickier. You have to remove the retainer disc, which will break it in the process. So you should get a rebuild kit (like $10 on ebay) with new discs. Some people have run without the discs, but I would not advise to, since they are used to hold the o-ring in place so that you don't have leaks.
When you go to put the injectors back in the fuel rail, and back in the head, lube the bores and o-rings with a little bit of oil to keep them from rolling and causing a leak.
*Snagged a couple pics so you can see what I'm talking about
Top of the injector, the tan ring is the "lip" I referred to
Bottom of the injector, with an intact retainer disc
Bottom of the injector, with a broken retainer disc