Hi hanna, Select Chart Settings, which is the sun-like symbol at the top of your window, and then select the Appearance upper menu. On the bottom left side you can uncheck the box for showing the Grid.
I don't think you can but a way to make them less clear is to make your entire application spacing to be tighter. Normal: Tight: You can do this by doing Setup(top right near the minimize, maximize, close button) -> application settings -> general -> look and feel -> spacing -> tight/normal/roomy