Once you select it, anything you do should apply only to the selected area, or you can create a new layer from the selection, too. So if you make a selection and apply levels, it should only change the selected area. The new layer gives you the option of going back later to change or delete your corrections.
For what you want to do you can also use the smart brush, which lets you select and apply corrections in one go. Just sort through the smart tool's options in the options bar's thumbnail's popout menu till you find what you want.
Try using the detailed smart brush (press the F key to tab between the two choices of smart brush)
From the dropdown menu choose lighting and double-click on brightness to select the thumbnail.
Then paint over the parts of your image you wish to adjust.
After you have painted to brighten your chosen areas, it’s possible to double-click the small red icon on top of the image. You can then tweak your adjustment using the sliders.
Barbara B. and 99jon, thanks VERY MUCH for the quick help; can't wait to try it out!