Here are a few quick commands that you can use to upgrade VirtualBox directly from the Linux CLI.

Check your current virtualbox version: vboxmanage --version

Add the virtualbox repository: sudo sh -c 'echo "deb http://download.virtualbox.org/virtualbox/debian $(lsb_release -sc) contrib" >> /etc/apt/sources.list.d/virtualbox.list'

Add the key: wget -q http://download.virtualbox.org/virtualbox/debian/oracle_vbox.asc -O- | sudo apt-key add -

Update: sudo apt-get update

Install the latest version: sudo apt-get install virtualbox-4.3

Check that you have the version you want installed: vboxmanage --version

And finally run virtualbox: virtualbox