Easy Peasy....
If the donut (stage 3) is attached to the firing can (stage 2), then the installation is nearly as simple as lubing the bolt.
On the assumption you know how to lube the bolt, which involves taking your Ion apart to gain access to the bolt and removing it, you basically just change over the firing can (with stage 3 attached) making sure you include the internal plastic ring which the firing bolt sits in from the old can to the new can, then just put in the new lubed firing bolt and then re-assemble.
If you don't put this internal plastic ring from the old to the new, when you gas it up it will just leak all the air from your tank out in about 20 seconds.
Also, If you find on re-assembly the firing can won't screw all the way on to the breech , it means you put the internal plastic ring the wrong way round.
I managed to do both of the above when I did mine......
After completion, you'll then have a good oppurtunity to adjust your dwell down to make your Ion a bit more efficient, but their are a squillion threads on how to do that on here.
Oh, if by chance your stage 3 isnt attached to your stage 2, you need a special tool that costs about a fiver to do the job in about 5 seconds, or you can fiddle about without the special tool for about half an hour and probably bend the c clip that holds it on.
I think thats all their is to it, and hope useful.