There are lots of tools out there to re-encode video and use all kind of filters to reduce noise, sharpen, etc. I haven't done this in a long time but used to use a tool called MeGUI (https://sourceforge.net/projects/megui/). Probably something better out there now like handbrake, etc. Personally I think it's a waste of time if you're starting out with a high quality source, but it's certainly something you can do.