How do I get rid of shadows on face photos for 3d models

[fast_cat]

I am trying to make up for the imperfect lighting conditions in a couple photos I took that I want to turn into textures for 3d models. The lighting on the sides of the nose, face, under the eyebrows, etc, are a slightly darker shade, and I have had trouble experimenting with the tools while being inexperienced with gimp. I would ideally like to have a brush which would lighten only a selected color. Thanks in advance for any help that I might receive.