replacing brake lines

This is my first post and had a question concerning my brakes. I have a soft pedal and I was wondering what could be some of the problems that would make this happen and I was wanting to get some info on replacing the brake lines. I have brake fluid on my brake lines near the calipers, this is a 96 tahoe with 188,000 runs great just wanting to get my brakes up to par. If there is anyone with insight it would be greatly appreciated.:banghead:

First wash off brake fluid and then watch for where the leak is.
Caliper piston or brake line or hose or bleeder screw?