Just like any other application window...click on the middle icon in the upper right corner. Application window is maximized if the currint middle icon is a double box. This is what you want to see and click on, which subsequently makes the application window resizable. Once you have the application (in this case Serato) set to resizable, put your mouse on any corner of the window until it turns to a double ended arrow. This will let you resize the window as desired.

DJKelly