It takes 1, you!
The cover is normally held on by 1, sometimes 3 screws. The screw is not visable form the ground. With a ladder you need to see the edge of the cover where it meets the skin on top. There should be a single screw there. There may be 2 more that go thru the rain gutter over the door as well. It depends on the light cover. Remove them and you can get to the bulb.
After you replace the bulb the screw on top should be put back in using a sealant so it does not leak. Parr bond is what I have used, vulcem is better, but an open tube is a hardend tube in a short time. Parr bond is available at many rv places. One tube runs about $10.00 and is re-sealable.
WBCCI #5501 AIR # 49
1978 Argosy 28 foot Motorhome
Wise men talk because they have something to say; fools, because they have to say something. -- Plato