Steps to Adjust the Screen Brightness
Enter the Home menu by pressing the Home button on the bottom half of the system. Look for a sun-shaped icon on the upper left-hand side of the bottom touch screen. Tap it. Select your desired brightness level. 2 is good if you’re in a dark area, whereas 3 or 4 is sufficient for a brighter environment. Remember, the higher the level, the faster your 3DS / 2DS’s battery will drain. Tap OK.
Remember, you can enter the Home menu and adjust brightness levels even when you’re in mid-game.
