Different models of cooker vary, but the general procedure is:
Switch off the electrical supply to the cooker
Move the cooker out from the wall, open the terminal box on the back of the cooker and confirm dead using a suitable voltage indicator
Disconnect the supply cable from the terminal box, connect the ends temporarily into a terminal strip and place that inside an insulated box
Remove the back cover of the cooker. Some cookers have further covers inside which must also be removed.
Locate the grill element terminals and remove the wires, making a note of how the wires connect. (Usually they are push on spade connectors)
Remove the fixing screws/bolts holding the element in place
Remove the element by pulling it out of the front of the cooker
Remove the new element from the packaging (it should be sealed in an airtight plastic bag) and insert the element into the cooker, so the terminals/bolts go through the same holes as the old one.
Screw/bolt the element into place
Check the resistance of the new element (should be in the 10s of ohms range), and check insulation resistance between the element terminals and the metal casing of the oven (10s of megohms at least, preferably 100s).
Connect the wires to the terminals in the same way as the old element. If the connectors are loose or damaged, cut off the old ones and fit new ones using the appropriate crimping tool.
Replace the back cover(s)
Set the grill control knob to on and thermostat to maximum (sometimes this is the same control), and repeat the resistance and insulation resistance measurements at the connection plate to the cooker.
Confirm that the supply cable is still dead and reconnect it to the cooker, replace the terminal box cover.
Put the cooker back in place, switch on the supply.
Wait for the element to heat up fully, check that the whole thing heats up.
Wait until any oil/residues have burnt off.
Check that the thermostat and other control knobs switch the element on/off.
Switch off.
Complete.
