Turn off power to the oven circuit. (check that the digital light has gone out).
In the case of a wall oven, slide the oven forward and with a person either side lift the oven onto to floor. Remove the screws from the back cover exposing the nuts to the heating elements. Carefully with pliers slide off the power terminals.
Undo the screws to the element. Reverse procedure after installing new element. [you cannot remove the element from inside the oven]
Steve Clayt, December 2009