The instructions should be in your manual if you have it but commonly there is a function key somewhere that you hit and hold down and then you would hit a corresponding function key (usually one of the number keys) that may have a picture of a circle with lines radiating out. kinda like a light bulb with arrows up and down. This will allow you to brighten/darken the screen. If you dont see anything like this go go gateways support website and look up your specific laptop model and choose to view the online manual, this should tell you more.
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