The settings are probably on the monitor itself, near the on /off button for it.

Mine has 4 or 5 buttons along the lower edge.
Press one and a text box with options should appear on screen.
You may need to press a few to figure out how to choose and select to make changes.
Or if you still have the book that came with it, it will tell you how to do it.

Or another way is to do a web search for your monitor brand name to get to the website for it, and then locate the model number there.
The manual should be there to download.