It depends on where the timeshare is, and if it is deeded real property or not, but if it is real property, in most states what you will need to do is prepare and execute a deed transferring the property interest into your son's name, record that deed with the county where the timeshare property is located, and then notify the resort of the transfer (paying them a fee, of course, to reflect that transfer in their records).
There are all kinds of variations, but this is a very basic outline of what - more often than not - the process looks like. If it is a 'points' timeshare, or a RTU contract rather than a deed, the process may look either slightly different, or perhaps even totally different. There are other kinds of factors that contribute to needed variations in the process as well.
We can help you more if you tell us what kind of timeshare interest it is, and where it is located.
Finally, does your son want the timeshare? If so, does he understand what the implications are?
Joe