I am using the Windows 8.1 Developer preview and running it through VirtualBox on my MacBook Air 2013 Model. I am wondering if anyone knows how to resize windows 8 to completely fit my screen, at the moment it is quite small on my screen making it hard to use but all of the preset screen sizes in Windows 8.1 don't fit the MacBook Air dimensions.
You need to install the Guest Additions to get a fully functioning display driver. After you do this, you'll be able to use Fullscreen and Seamless modes.
To install Guest Additions, click on the Devices menu and select "Install Guest Additions".