Unhook the power running into the light fixture before attempting to remove the ballast or any other part of the fixture.
Put on a pair of insulated gloves and remove the covering from the light fixture.
Unscrew any existing bulb or tube light and place it gently aside in a safe place.
Locate the ballast on the fixture. The ballast in a tube light is often located on the far end, near where the wiring enters, but is sometimes more centrally located.
Carefully clip the wires that are attached to the ballast, leaving a good amount of excess if you ever plan to rewire it, and then look for the fastening screws that hold the ballast in place.
Unscrew any fasteners that are holding the ballast in place to finish the removal process. Some ballasts may be clipped into place, requiring no tools to remove. If this is the case for your ballast, simply slide it in the opposite direction of the clips to remove it.