How to change the grass?

Well , I did play a bit with the textures and such , but I can't seem to find out how I could possibly change the grass for example to Dirt , or another example , that was the first thing that came to my mind ,I did look around the forum but I could not find anything concrete.

I just need a tip on where to look , I don't the hole thing explained if anyone would be kind to help I would appreciate it. Thanks.

I hope I post in the right section.

Bump . Anyone ?

Well, I know that you can change the textures of water from Data.pk2. Not sure exactly where grass is, but I'd guess somewhere in there. Sorry, I don't do a lot of texture editing.

Do you mean like this
I know it's pretty easy in a way but what do I get for telling you ;o changing all the texture will be ugly as f***.