|We need the make and model of the computer to properly help.|
If it has a separate monitor it might have controls on the front.
Otherwise there could well be controls in your display card settings, via Control Panel. They could show as color settings.
Another possibility is that there is an F key provided for this.
So, without the info it is a big guess because we don't even know if it's a laptop or PC.
Always pop back and let us know the outcome - thanks