Consider, you don't need to do anything; for a 14 team league your hitting is good. And JD Martinez in the minors put up monster power numbers, far superior to Jenning's minor league career. I'd take Jennings over Martinez, don't get me wrong, but you have plenty of hitting. I'd recommend if you move Youk consider trading him for some pitching if you need it.
Position players, between Jennings and Youk, normally I'd say 3B is much more difficult to find production from than OF, plus youkilis is a staple, very good fantasy 3B production.
If you pull the trigger on the trade, you'll putTrumbo on your team for 3B, (You cannot afford to put Young there subbing in Neil Walker's crappy production, you'll lose too much).
I just see you utilizing Youkilis' value for something you need rather than another OF in Jennings.