Editing Tomb Raider 1 Texture with Gimp

Hi all, i need to know whats the best way to edit Tomb Raider 1 texture pack directly in game, i have png images ready for editing and Gimp, do i need to use bump map in Gimp or other options to get beautifull graphics. Thanks.

What’s this have to do with Unity?

Not related to unity. Closing.