Another way you could try to brighten up the dark area is to press Ctrl "j" to make a copy on a new layer then change the blend mode of this new layer to Sreen.
Now hold the Alt key and click on the layer mask icon to mask the layer.
Select the brush tool make sure the colour is white and pain over the dark areas with the white brush, if you paint over an area by accident press ctrl "z" to undo or chage the brush colour to blackand paint over the area again.
Once you have painted over the dark areas it might look too bright just adjust the opacity untill you get the results your looking for.
The great thing about using a layer mask like this is that it's non destructive the changes aren't permanent until you merge them down onto the layer below.
Hope this helps