No big deal. Go to Google, search GIMP. It should be one of the first things that come up. Download, install, and you are ready to go. It is completely free, and it is what I use. If you ask Hawkza, he is putting together a modding startup kit, I am sure he would send you what he has so far. I wrote a brief instruction manual for GIMP for him, so you could follow it to do what you want. Also, I can tell you anything about GIMP that you would like to know.
I would just make the changes for you, but I am just too busy with my own stuff right now
