Hold the camera as you would taking a shot. Look at the top of the lens. Are the two red lines below the aperture/shutter readings at the very top? If so, pull on the metal tab on the right side of the lens and turn the shutter speed dial. As John pointed out, the shutter/aperture rings are locked at a certain exposure value, some combinations of which prevent you from turning the rings. Try moving just the one ring, and after it's changed you'll probably be able to move both again.