There are a couple of ways to cut the CI: a snap cutter (you can rent one at most places - looks like a large, weird bicycle chain with a rachet to tighten it up), a grinder, or a saw. By far, the fastest is the snap cutter. You'll need enough room around the pipe to use the tools. Underground, you can use the rubber sleeve with hose clamps. Make sure to backfill carefully so the pipe ends are well supported and stay aligned.
If the pipe is cracked, you may want to go to where it meets the main line. If you do, then you'd need a different method to fix it....Fernco makes special rubber dognuts that fit into the hub and then the pvc is a compression fit inside of it. Problem is, not all pipes are the same, and the local shops may not carry the exact size you need. Alternative is to cut that part off and replace with pvc, or get a plumber to relead in a new piece. If the CI is solid, you don't need to cut back that far, and this is a mute point.
Problem is, you won't know until you dig it up the condition of the pipe or fittings. On a good day, it is farily easy, on a bad one, you could be replacing a lot more than you think now.