Try these tutorials with Photoshop
Edit photos to create new images and graphics.
Adjust brightness and contrast to improve a dark photo.
This video expands on your basic knowledge of adjustment layers to show how to adjust lighting in a photo.

Increase the brightness of a dark image with a Brightness/Contrast adjustment layer.
Increase contrast in a washed-out image or decrease contrast in a high-contrast photo with a Brightness/Contrast adjustment layer.
Examine different styles by increasing and decreasing contrast.
You'll get step-by-step instructions that guide you around the interface.