How do I update a file that has already been published?

I'm trying to change the downloadable form on my page to an updated version, I have uploaded it into the system (file storage area). When I choose the link to pick it, it says it has been selected (as that's the page that will be downloadable to the public). but when I go to the page preview (after I hit save) and and published the page. The form that pops up to download is the old one. I've tried redoing the button from scratch, re-uploading the new form, and nothing seems to be working!