Hi C,
changing a light bulb is not dangerous as long as you are familiar with electrical safety. Remember microwave ovens run at 4000 volts and their circuitry can under fault conditions store lethal voltages months after being unplugged. Sad to say this is a job best left to a tech. If you insist on proceeding and do not understand electrics there is no point in me telling you how to discharge the high voltage capacitor, it may only lead to further possible danger. So as I say if you insist on proceeding, first DISCONNECT THE APPLIANCE FROM THE MAINS, second, remove the outer cover, Third, TOUCH NOTHING OTHER THAN THE LAMP. The wire connectors may have locking tabs so take care in removing them, then simply remove the lamp an replace,
kindest regards
patrick
microwave-repairs.co.uk
patrick, April 2009