Turn off the gas and power supply to the Hotpoint oven. Take out any oven racks, and remove the oven's bottom pan by removing its retention screws at the oven's rear. Also take out the flame spreader by first removing the wing nut that holds it in place.
Take out the ignitor's mounting screws, and then pull out the ignitor's connecting plug--by hand. Discard the old ignitor.
Place the new ignitor in position and push into the connecting plug. Then screw into place the mounting screws.
Turn on the power and gas to the oven. Turn on the oven, and check the ignitor: if it lights in 30 seconds or less, it is working fine. Turn off the oven, and replace the flame spreader, bottom pan and any oven racks.