I want to add insulation beneath my attic floor, but I'd have to pull the attic floor up to do it. How will this effect my second floor ceiling? I am worried that the ceiling beneath it is protected by the attic floor.
Certainly your attic floor protects people from stepping through the ceiling beneath it, since that ceiling is not designed to hold weight much heavier than the weight of insulation. But you probably don't need to remove your attic floor to insulate the space. You could simply lay insulation above the attic floor - unfaced fiberglass batts, specifically, laid over the floor in the areas you wish to insulate. If you use your attic for storage, consider consolidating those stored items and keeping them in one area of the floor that you leave exposed.
Now, if you presently have no insulation whatsoever between the attic floor and the second floor ceiling, take that floor up and insulate it - and restrict the workzone to responsible adults who know where they can and can't place weight. But if you simply need more insulation in your attic, the easiest bet is to put it over the attic floor.