Under Ubuntu, installed packages can be updated to their newest version via apt-get, following the same process as if you were initially installing them.
To update a package, first, make sure that the package index on the server is up to date by running:
sudo apt-get update
Next, the package itself can be upgraded to the newest version with the following command, replacing PACKAGE with the name of the package:
sudo apt-get install PACKAGE
If the installed package is already the newest version available, the
apt-get command will state that in its output.
The full usage of the apt-get command can be viewed at: