The top will come off by either unscrewing screws in the top frame of the door or by releasing clips that hold it to the front by inserting a screw driver.

You will then see safety thermostats on the heater housing which you need to test for continuity.

If they are ok, take off the front and test the thermostat on the blower housing. Finally, take out the drum and check the heating element. I have found these tend to break rather frequently on the GE's.