Texture Editing

Texture editing is a mostly creative task involving extracting textures from the game and editing/re-drawing them in your favorite image editor, or creating entirely new textures to use in the game.

Texture editing is mostly a creative practice, and requires very little technical expertise to do successfully.

BLPLab is a popular tool for converting between BLP formats

Photoshop CS6 is another popular tool because it has a plugin for loading BLP files directly.