Keeping your computer up to date is the single most important task for protecting your computer. You can review the Ubuntu Security Notices (USNs) for more information on published updates.
By default, Ubuntu will alert you when updates are available for your computer and updates are handled through Update Manager. By default, users are notified daily for security updates and weekly for non-security updates. How and when Ubuntu alerts you can be configured in Update Manager. You can access Update Manager anytime by pressing 'Alt+F2', entering update-manager and pressing Enter. Its settings can be adjusted by pressing the 'Settings' button.
Once Update Manager is open, you can review and select pending updates as well as check for new updates. Simply press the 'Install Updates' button to upgrade the selected packages to the updated version.
In Ubuntu 10.04 LTS and later, Ubuntu will alert you when updates are available for your system when you login. While this information is typically updated daily, you can check for and apply new updates with:
$ sudo apt-get update $ sudo apt-get upgrade
Under some circumstances running the above will not apply all of the updates, which can happen when new packages provided by the update are to be installed. If this happens, you will want to run sudo apt-get dist-upgrade, review the output being careful to note any package removals, and confirm that you want to apply the updates.