VirtualBox includes full support for a variety of Linux operating systems, including Ubuntu. Once Ubuntu is installed, the default resolution won't increase past 1024 by 768 without additional tools. The VirtualBox Guest Additions add functionality to the installation. The guest tools let you increase the resolution dynamically by resizing the virtual machine window, share a clipboard with the host operating system and share files and folder with the host system. The guest tools are included in the Ubuntu package repository.
Open VirtualBox and run the Ubuntu virtual machine. Log in with a user name that has administrative rights.
Click the "Dash" icon at the top of the menu on the left side of the screen. Type "Terminal" in the search box. Run the "Terminal" application from the search results.
Type "sudo apt-get install virtualbox-guest-dkms" without the quotes and press "Enter." Wait for the installation to finish. The screen resizing, clipboard sharing and folder sharing features are now activated.