Are you asking about brightness as viewed on the LCD, or are you asking about increasing brightness on the actual image taken? If it's the image, there are two special modes that you can select on your mode dial. They are "Night Scene", "Night Snaphot", and "Indoor". A description of both, along with your camera's other special settings, may be found here:
"Night Scene" can be selected directly from the dial. It's the one showing a person standing under a star. Note that Night Scene should be used with a tripod to reduce the potential for blurriness.
"Night Snapshot" works almost as well, but does not require a tripod. It can be accessed by selecting SCN on the dial, and then pressing right or left with the selection buttons until it shows in the menu. The camera will remember this setting the next time you select SCN. I usually keep my camera always set to this setting so that I merely have to select SCN to use it.
"Indoor" works very well in those large rooms that may produce dark backgrounds when taking photos. It also does not require a tripod. It's accessed the same way as "Night Snapshot" (Select SCN, then right/left until selected). This is another good setting that I like to keep sometimes set in SCN.
Try all three settings, (and don't forget all the others too). Think you'll be impressed.