Actually, you are expecting something dificult. do not exist what you want. Simply put, some programs might be able to fix some of your problem, yet the main is the source.
try looking for higher resolution videos and stop thinking low res to high res is possible because is not.
Trick one: MOre moving images = less quality
trick two: Fix color or background = gain more quality
trick three: a commercial soft its more likely to help gain some quality, a least 10% more than a free soft
trick four: your computer might be not fast enough, basically, memory and CPU usage is 95-100% in use while converting, will also affect quality.
trick five: a video should be good enough befor converting to assume better conversion. ie, if video on player looks nice, try to double the size to see how it looks, if quality keep on this move then is ok to convert; mostly that is how it really works! if it does look pixel like(square full of one or more colors in fading) then conversion is worthless.
This is a free tool, please read and look for info and manuals in your favorite search engine