For beginners, transforming a texture 3D model usually involves 4 basic steps: export the model with textures, edit textures in 2D software, reapply via UV mapping, and test/render.
Export the model (e.g., OBJ format) with its texture files (PNG/JPG) to keep UV links intact. Edit textures in free tools like GIMP—adjust colors, fix flaws, or add details. Use Blender (free) to reapply the edited textures to the model’s UV map. Test with previews or simple renders to check how the textures look on the model.
If you’re new, try Blender’s built-in texture painting tool first—it lets you edit textures directly on the model, so you don’t need to switch between 2D/3D software, making it easier to learn.