Turn off the gas and power to the oven. Open the oven door and pull it up off its hinges with both hands. Place the door to one side.
Lift up and pull out the oven floor. Unscrew the wing nut holding the gas burner cover in place, and take it out.
Untwist the two ceramic nuts holding the ignitor/oven wires together. Put the nuts to one side, and separate the wires. Remove the screw holding the ignitor and metal cover in place, and take out the ignitor.
Put the new ignitor in place and tighten its screw. Attach either ignitor wire to either oven wire with the ceramic nuts. Turn on the gas and power to the oven. If the ignitor produces a gas flame after a few seconds, it is fine. Turn off the gas before replacing the gas burner cover, oven floor and door.