Turn off the gas, if removing the fitting from a gas pipe. If the pipe has electrical cable in the middle that supplies the fixture, turn off the power to the fixture.
Hold the pipe next to the fitting with one hand. Turn the fitting counterclockwise with the other hand, until the fixture is removed.
Place a wrench around the fitting if it won't budge, and a second wrench around the pipe, close to the fixture. While holding the wrench handle securing the pipe, turn the other wrench counterclockwise. When the fixture loosens, take off the wrenches and remove the fixture by hand. If it is attached to electrical wires, unscrew them or sever them with pliers.