While the pic is opened in Photoshop;
IMAGE >> Shadow/Highlight This will give you some play around with it in certain areas.
or
While image is open : LAYER >> Duplicate Layer >> OK >> go to the image toolbox on right side of screen where you see the step by step history of the image you are working with >> Click drop down box besides NORMAL and choose MULTIPLY.
It will darken the pic some and you can slide the Opacity level back and forth to get the right contrast. Just remember to flatten your image >> Layer >> Flatten Image >> before saving so you can save the image as a .jpeg