1. Get a picture, any picture.
2. Go find caster.
3. Right click caster
4. Click on show properties.
5. Click show local files .
6. Find any texture.
7. Look at the textures name
(Every textures is either a jpeg, bmp, or png.)
8. Rename your picture the name of the texture you want to replace.
9. Put file in the game (if it says replace click yes)
10. Run the game


Ta-da, YOU DID IT!

BONUS STEP: Post your screenshots here.