Remove any ceramic-glass tops or vent grills and filters present on the surface of the Jenn-Air range top by lifting them out of place and setting them aside.
Cut the power supply at the main circuit breaker by switching the circuit that controls the range top to the "Off" position.
Open the cabinet beneath the Jenn-Air range top. Clear out any objects in the way so you can access the blower and connections to the electrical or gas, if present.
Locate the gas-supply valve underneath the range top in gas models. Turn the valve to the "Off" position. Unscrew the gas hose.
Locate the blower, which is the large, circular device to the side underneath the Jenn-Air range top. Disconnect any venting attached to the blower. The venting is held in place with clamps, strips or tape.
Locate the junction box where the wiring from the range top is connected. Remove the junction-box cover. Unscrew the wire nuts on the end of the wires. Test that the electricity is turned off on the wires with a voltmeter. Once you've verified the electricity is off, separate the range top wires from the house wires by pulling them apart.
Loosen any clamps on the underside holding the Jenn-Air range top in place on the countertop above with a screwdriver or wrench, as needed.
Have an assistant help you lift the range top up and off the countertop.