Here is a guide to install VirtualBox 4.2.0. If you have VirtualBox 4.1 (or an older version) installed you first need to remove it from your system.
VirtualBox is a powerful x86 and AMD64/Intel64 virtualization product for enterprise as well as home use. Not only is VirtualBox an extremely feature rich, high performance product for enterprise customers, it is also the only professional solution that is freely available as Open Source Software under the terms of the GNU General Public License (GPL) version 2.
To remove VirtualBox 4.1 open a terminal window (press Ctrl+Alt+T) and copy+paste the following line:
sudo apt-get remove virtualbox-4.1
If you have an older version installed replace -4.1 for the version you have installed.
To install VirtualBox 4.2.0 copy+paste the following lines:
echo "deb http://download.virtualbox.org/virtualbox/debian $(lsb_release -sc) contrib" | sudo tee /etc/apt/sources.list.d/virtualbox.list
wget -q http://download.virtualbox.org/virtualbox/debian/oracle_vbox.asc -O- | sudo apt-key add -
sudo apt-get update && sudo apt-get install virtualbox-4.2 -y
When installed close the terminal window and download the VirtualBox 4.2.10 Oracle VM VirtualBox Extension Pack from this page. To install the extension pack just double click the downloaded file and it will be installed. To start VirtualBox click on the Dash Home button and search for: virtualbox