Again, simply click the brush and start to paint the foreground areas where you'd like to reveal the bottom layer. Another option to achieve the same effect is to click the '+' then 'Add an Adjustment Layer' and choose something like 'Dramatic.' Then you can once again reveal elements of the layer below using the brush. A third way to adjust selected areas in the same picture, is to use a 'Luminosity Mask,' found by right clicking a layer. This automatically masks the darkest parts of your picture so you can control highlights. If you want this reversed, simply right click on the mask and click 'Invert.