Ubuntu uses the apt package management system which makes updates and upgrades pretty simple.
When logging on, ubuntu summarizes available updates. Use the following to do the updates:
sudo apt-get upgrade
Note, though:
However, if you want to upgrade, unconcerned of whether software packages will be added or removed to fulfill dependencies, use the ‘dist-upgrade‘ sub command.
Many more apt-get commands are summarized in 25 Useful Basic Commands of APT-GET and APT-CACHE for Package Management.
‘man apt-get‘ or ‘man apt-cache’ are also useful.