If there's no obvious removable cover over the bulb (and the owner's manual doesn't address it) some disassembly may be required.
I have a diagram
at my site which helps you find & replace many GE cooktop and cavity light bulbs. Other models are similar.
You can find helpful exploded view diagrams and for many brands by entering your full model number here: http://tinyurl.com/gv383
Always unplug a microwave before removing or installing any bulbs.
If it's an over the range type, remove the vent grille across the top and see if bulbs can be accessed there.
There may be a panel on the bottom covering the light(s), instead.
If not, chances are you'll have to remove it from the wall, then remove the outer cover.
If so, the installation instructions are very handy, and it's best to have two people since the microwave can be heavy and awkward.
Once your over the range type is out of the wall, or if yours is a counter top model, the outer cover (wrapper) will need to be removed.
The screws you need to remove should be pretty obvious, and a special driver (such as a T20H Torx type or GTXH20-100) may be needed.
Be sure to put all the screws back in the right holes, since some may be special grounding screws.
Bulbs can be had in most grocery stores, hardware stores, home improvement centers, and big box or department stores.
Many models use halogen lamps. You must not touch the new one with your bare skin, as the oils will shorten the bulb life.We're happy to help and we appreciate your thoughtful rating of our answer.TO BIGDEEL
Do you mean your internal cooling fan or the hood / vent / exhaust fan?
If it's ther internal cooling fan, do not use the microwave or the magnetron will overheat and be damaged or destroyed.
We're happy to help and we appreciate your thoughtful rating of our answer.