With all due respect for your desire/need to remove and replace this line, I gotta tell you that it isn't galvanized pipe. It is cast iron. Cast iron is much heavier than galvanized pipe and poses real challenges for a novice. I do realize that like all of us DIY folks, you are looking to save the cost of a plumber. Nothing wrong with that and perfectly understandable, but perhaps this is not the place to try to save money. When you start cutting cast iron loose, you are opening a can of worms. A plumber not only has the proper tools to do the job, but more importantly, has the experience to do the job properly, safely, and quickly. Not all jobs are suited for DIY and working with cast iron is one of them.