These are the questions you need to get answers to. Think back to the 1970’s, if the floor could support a water bed then it will support a large safe.
If you are really worried about weight you can always help distribute the weight over a larger area by placing the safe on sheet of 3/4" (min) of plywood (not press board) put down the sheet so it spans across as many floor joists as possible and center the safe on it. This might be a little over kill but if it gives you peace of mind then that’s what counts.
I forgot to mention the closer you are to an outside wall the more strength the floor will have.
Yep, those questions first. You can mitigate the weight by spreading it out, as DBrogue said. Also, I place them where they joists have hangers, so an outside wall, or interior if I know there are hangers there. I have a dang heavy safe, and so far have not had any issues other than moving it.
If you are on the second story, the weight of the safe will be some of your limit, and the how many bodies does it take to get it there.
What type of storage do you have now? Do you know the weight? If you could split the load between two or more safes you may be able to solve the problem quickly. If you store ammo in one unit and firearms in another this could also help the weight sitution. Have you thought of an under bed storage,much larger area? The statement about locating the safe near an outside wall is a very good one.
In searching for an answer I came across an excellent USCCA article on this very topic. Spoiler alert…you should be fine as long as the stairs leading up to the second story are solid…and use a moving company to be, well safe.