On this style of light fixture, you'll usually find that one of the three clips is spring loaded and can be pulled horizontally away from the center. This allows you d to remove the glass. There is no need to unscrew the clips.
I learned a little about these doo dads this year when the two on our home started leaking after the winter freeze we had in Texas. The rubber grommets inside both went bad. After trying to get them off with no success, I took a picture and headed down to my favorite plumber dude on isle 9 at our local Home Depot. He laughed and smirked a little, then told ...
If you're talking about the metal-colored screw that sticks out parallel to the ceiling, use a nut driver:
(image from Klein Tools via Google)
on this hexhead (not "flat head") fastener. They're available in many sizes, and you'll need one to fit this fastener head.
Props to @brhans in comments.
Well, you could try one LVL and if it collapses, then rebuild the floor and use two.
It really depends on how much stuff you have in the room above and how solid you want the floor to be. Do you care if the floor bounces when you jump up and down?
I doubt that a 20 foot wall is not load bearing. What is holding up the roof? If you go into the attic, are ...