I am new to texturing these models too, but the simplest way that I have found to re-texture an existing entity is to open the DDS file, with a program such as photoshop, then change anything you desire, making sure that you keep everything where it is supposed to be (eyes, nose, mouth, etc.).
Give your new texture a specific name and save it as a DDS file then when you run fps creator, choose your character and apply the texture you made for it.
Hope that helps You can check out my threads to see what I have done, it may give you ideas.
Gary