i to all, there's a best way to light up a face that is under expoxed because it was take against the sun?? :)

It depends how much information is still held in the image. Was this shot in RAW? if so you maybe able to gain back some of the information using ACR. If not you can try various approaches. One initial approach is duplicate the layer and change the blend mode type to Screen, this in effect gives an appearance of increased exposure. Then either delete or mask the areas (not the face) that are not required.

You can try shadows and Highlights Image>Adjustments>Shadows and highlights.

If you can post an example of this we can help you better.