First un-plug the W/D from the mains electric. Many of these have a thermal reset button under the lid. (Usually with a little red cap) It usually trips because of fluff blocking the airways or dryer fan motor, or the fan motor is jammed or has stopped working, causing the element to overheat. If it has tripped, find out why. It won't have gone without a reason. I have never had to replace an element in one of these.
Freddo, February 2009