Disconnect the lamp module from the ballast (pull do not twist). Remove the clamp band from the lamp module and use a flat head screw driver to remove the lens and gasket (push in gently so lens does not chip) example like opening a can of paint). Change the lamp. Before closing the fixture, remove debris from the screw holes or under the gasket or lamp housing will not seal properly. Also, ensure when closing the lens and gasket that it is a dry environment to prevent moisture (moisture trapped inside the lens can damage the reflector) and ensure the gasket is sealed properly and tear free. moisture trapped inside the lens can damage the reflector) Install the screws and tighten evenly.