Ubuntu (and Debian) software can easily be updated using the apt-get command line tool.

apt-get can be used from a terminal window as follows:

• apt-get update: Update is used to resynchronize the package index files from their sources over the Internet.
  To retrieve updated software list, enter:
  sudo apt-get update
• apt-get upgrade: Upgrade is used to install the newest versions of all packages currently installed on the system.
  Update software, i.e. apply updates:
  sudo apt-get upgrade
• apt-get install <package-name>: apt-get install can be followed by one or more packages desired for installation. If package is already installed it will try to update to the latest version.
  To upgrade individual software enter apt-get install followed by the software name, as follows:
  sudo apt-get install <package-name>

apt-get update, apt-get upgrade and apt-get install will all retrieve files over the Internet. The location of update pages is specified in /etc/apt/sources.list (repositories). Unless you need extra repositories for your setup there is no need to modify this file.

Using Ubuntu Update Manager Tool (GUI)
The Ubuntu Update Manager Tools works like the Microsoft and Red Hat update manager tools.  In the Ubuntu GUI you will see a little icon in the task bar when updates are available. Just click on it and follow the online instructions.

You can also start the Update Manager GUI tool by clicking System | Administration | Update Manager.