How do I increase/improve brightness?
Please reword your question? Which brightness do you want to increase? Your screen? Images in a document? Contrast of text vs. background? What is your task?
As as always, mention OS name, exact LO version (with at least 4 numbers) and save format.
Brightness is usually a property of your physical screen and adjusted with physical keys or a settings menu of the screen.
Depending on manufacturer and cables there may also be a software for windows or Mac, sometimes you can calibrate the screen.
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In some professional settings the calibrated settings can/must not be changed.