After 5 igniter replacements, I've gotten pretty good at this. Less than 30 minutes start to finish -- including mopping under the range, etc. You need one hex driver for the whole job -- 3/8" I believe.
1. Remove all of the racks and the oven door. Remove the bottom panel inside the oven. Now unscrew the flame cover (4 hex screws), remove, and unscrew the old igniter (2 hex screws).
2. Pull the oven away from the wall. Be careful not to kink the gas line. Unplug the range. Remove the rear panel (about 8 hex screws). Disconnect the wires to the old igniter. My wires were connected with wire-nuts, yours may have a molex connector. If you have wire-nuts, you need to clip the molex connector off the replacement igniter and strip the wires back 1/2".
3. Remove the old igniter from the oven side. Feed the wires for the new igniter from the oven side through the back wall. At the back of the range, connect the wires using wire-nuts or the molex connector. Be sure there is no bare wire visible that could short.
4. Replace the back panel. Plug in range. Move range back into position. Screw in new igniter. Turn oven on to be sure the igniter glows red (takes about 30 seconds). Replace flame cover. Replace lower oven panel. Replace oven door and racks.
5. Done