Before you can alter the settings of a virtual machine, you must first have the machine powered off. Load VirtualBox on your Mac desktop and make sure it is powered off on the left hand panel. Double-click General and a window should pop up allowing the changing of several settings. For example, you can include a description to keep many virtual machines separate, or adjust the size of the drive. You can even add virtual devices through ports if they are connected to the physical machine. The option to virtually share files can be very nifty if you want to store information on both the physical machine and the virtual one.