Juan.
I don't think your picture is in need of some shadow highlights. My advise is you will have to adjust histogram properly with
PS' levels tool. I've tried a go with it, hope you don't mind. It's quality reduced just for storage purposes, but you'll see what I mean.
You have a big gap on the original histogram on the right -white- side and the left -black- slider is not showing a pure black on the picture. I suggest you to adjust levels for every RGB channel instead of an overall histogram correction, you'll get rid of some blue cast as well.
Nice picture, BTW!!
Stil