Find "Brightness"
Slide your finger down the display starting from the top edge of your phone.
Press the settings icon.
Press the settings icon.
Press Display, gestures & buttons.
Press Brightness.
Set display brightness
Press Automatic brightness to turn the function on or off.
If you turn off the function:
Press and drag the indicator right or left to set the display brightness.
Press and drag the indicator right or left to set the display brightness.
Press OK.
Return to the home screen
Press the Home key several times to return to the home screen.