Instructions
Put the Nikon D80 in manual or semi-automatic mode because the automatic mode on the Nikon D80 contains preset ISO instructions that cannot be altered.
Press and hold the checkerboard/magnifying glass button on the back of the camera. This button is marked "ISO."
Turn the thumb dial located on the back of the camera to change the ISO. The D80 has ISO settings ranging from a low 100 to super sensitive 3200. Monitor your changes using the camera's LCD screen.
Look through the lens and view the in-camera light meter reading. The changed ISO will affect your meter reading -- when the meter gauge is balanced in the center, your exposure settings, including ISO, are correct for the light entering the lens.