My friends plumbing system is damaged, and he needs to get a new one.
If you have to ask how to do something like that, you shouldn't be the one doing it. This is something that needs to be done by a professional, or someone with experience. No offense.
The whole system? If you don't already know how, I strongly suggest you get a contractor in to do the work.
If you don't already know how don't try it, have a plumber do it