Light has burnt out - Sharp R820BK 900 Watts Convection Microwave Oven

R-820BK/BW Microwave Operation Manual
Due to the risks of death or serious injury the above owners manual suggests that a burnt out light demands a service call by a qualified technician.
That said, if you have a basic level of competence and read the safety hazards involved with microwaves (see a good resource on microwave safety and repair at:
http://www.kellerstudio.de/repairfaq/sam/micfaq.htm
Often, the microwave is divided into two main compartments, the electronics compartment(usually immediately behind the front control panel), and the high voltage compartment(usually behind the electronics compartment). The light bulb is likely in one of these two primary compartments. If it is in the high voltage compartment with the HV Capacitor and magnetron, changing the bulb becomes much more dangerous.
Please be very careful if you do decide to do this on your own... unlike most electronics microwaves can remain lethal, even when unplugged. Hope this helps.