The problem is, there is no perfect upscaling technique, as it implies to create something that is not there!

Said so, there are some methods better than others, but to obtain good results you have to study them... if you have a lot of patience and time to dedicate to video editing, my advice is AviSynth; if you have less time and patience, try VirtualDub (and VirtualDubMod too)

They are both free, and have many filters; between them there are many upscaling ones; my preferred software is still Avisynth, though; in particular, there are many more upscaling filters to choose!