It depends on the appliance age and model number.
Older machines had the element fitted in the front of the plastic drum (secured with a 10mm nut). To replace, it's neccessary to remove the appliance front panel.
Newer machines have the element fitted in to the rear of the plastic drum. On these, it's neccessary only to remove the lower rear access panel to gain access to the 10mm securing nut. Once you've removed the 10mm nut, push the threaded post back in to the heater as far as you can (to relieve the compression on the rubber seal). The heater should then come out with some persuasive ' wobbling and walking'.
Might sound like a silly question, but how do you know the element has failed? These are normally pretty good.
Hotpoint Man, February 2006