Familiarise yourself with the topside (the opposite side of the connections) of the thermostats at the rear so you'll know what your looking at when you see it.
Then lying on your back stick your head inside the door of the dryer you will see the front thermostat straight away.
(Alternatively you can just run your hand behind the rubber seal of the door to locate the thermostat But I have always found the things that you do whilst lying on your back so much more fun ;)
To change it, remove the two screws holding it in place and pull it down to reveal the connections at the back.
Use a pair of long nose pliers to secure the connecting wires (and to aid in reconnecting the new thermostat) and pull the thermosat down firmly it might be quite tight so be persistent the thermostat will come loose from it's connections.
(In my case I didn't use the pliers to hold the connections and once freed from the thermostat all the wires shot up into the tumble dryer and were an absolute bugger to retrieve!!!! You have been warned).
When you remove the thermostat make a note of which wire was connected to which side of the thermostat so you can connect the new thermostat in the same way!!!!
(Having said that both of the wires are the same colour so i'm not exactly sure it matters on which side they are connected but it's always better to play it safe!!!!!)
Then reverse the steps to add the new one!!!!!
Tymon Hall, September 2006