Two ways, go to System Preferences > Dock and you can adjust the size, adjust the placement and adjust the amount of magnification.
Or, there's a slight divider in the dock for apps and documents/folders. Click on that and hold the mouse down and you can drag the dock larger or smaller.
You can also look into hiding the dock until you need it (just dragging the mouse to the bottom of the screen (or sides if they dock is there). Saves space on a 12.