The only thing I can add to that is to check whether people have made a Jelly Bean custom ROM for the phone first, since that is how rooting helps: you can install custom ROMs, and often these include more recent Android versions than the manufacturer has released. But you still need someone to have made a suitable ROM for your phone model.
The good news is that a quick web search for "galaxy s duos jelly bean" turned up a number of results, so I think you could indeed get what you want this way.
