1. You need to know the texture number of the shirt which is 524 and the pants 3.
2. Open the 2kX Mod tool and locate for the shirt texture.
3. Export it and edit it to your liking.
4. If your done editing import it back and see the difference!
5. Enjoy
Guys for the pants it is the same procedure except you need to look for #3 texture number than #524 which is the shirt