Converting will in fact reduce the quality of Video and Audio. If you wish to avoid this, one other option is simply change the container type.
It would be easier to make a suggestion if we knew the exact Video and Audio codec used inside that container.
However, one thing you can try is YAMB
Youll also need MP4box
All that you'll need to do to setup YAMB, is extract it, and MP4box to a folder.
Open YAMB, and in Settings, select the location of the MP4 box.exe so it knows where to look.
Then you can Re-Mux with it.
Just choose to create a MP4, and for Video file and Aduio, add that video.
This will create a MP4 that Windows 7 supports by default, and will NOT recode the video.So there will be no quality loss, and takes just a minute or 2.
This will work if the file is 4GB or less.
If it is over 4GB in size, MKV container would be a better choice.