Aquariums: Changing Substrate

When I first got into fish keeping I didn’t know anything about Cory’s and set my tank up with gravel. I know now that sand is better so that the Cory’s can sift through it. With the current gravel they can’t do it at all.

So I’m wondering if changing the substrate is a good option? I’ve seen videos of people doing it, or just adding sand on top of the gravel and calling it a day. But I’ve all heard that doing that can be dangerous because getting rid of the gravel is getting rid of beneficial bacteria and also potentially trapping ammonia pockets or bubbles.

Has anyone ever replaced their substrate? Any advice of what I should do? Either changing the gravel to sand, adding sand on top, or just leaving it alone? Thanks for any advice!