Hey bud,
Here's 2 possible solutions for 'ya
First off, in Photoshop you can open your image, then go to Image > Adjustments > Brightness/Contrast for the quick lighten/darken effect. Also while your in there check out Image > Adjustments > Variations to mess with different color hues (kinda cool).
Next up, an alternative to PS for the quick lighten/darken adjustment would be
Irfanview. Open your image then go to Image > Enhance colors (Shift+G on your keyboard). there's a few sliders in there that should do the trick for 'ya
Hope this helps