Is there any tool or software that can converts a video from low quality to high quality? Like a 3gp.
I personally suggest Apowersoft Free Online Video Converter to convert into HD videos.
In my personal experience I used Pavtube Video Converter, it's really nice. We can adjust any video up to 1080p video in the conversion.
The tool for me to convert videos is DRM media converter. Since all iTunes videos are in M4V, which DRM protected, making it impossible to be played on non-Apple devices. So the only way for us to enjoy iTunes purchased or rented videos on Windows movie maker, android phone and other devices is to get rip of DRM protection at first. This program is designed for iTunes users to crack DRM protection and convert videos from M4V to MP4 at 30x faster speed with zero loss quality. Now there is a Christmas discount sales of this tool, you can check more info on here. Hope this tip is useful to you. Good luck.
I guess converting a normal Video to HD format will not happen, you can change the format to another, but High Definition I’m sceptical. Off course you know high quality to lower quality is possible, but to do in reverse will not restore the low quality to a high quality.