Upgrading Aegir is designed to be as easy as it possibly can be, and regularly improves over time as the developers attempt to streamline the process for users.
Nonetheless, the upgrade process can seem a little daunting to users. This is mainly because some expectation arises that because Aegir is built on Drupal, and is made for managing Drupal sites, it seems reasonable to expect the upgrade process to be as straightforward as, say, upgrading a regular Drupal site.
Aegir is a powerful system that goes beyond a normal Drupal application by being split into two parts: a frontend (the browser-based control panel) and the backend (bits on the system in /var/aegir, such as Drush and Drush extensions), along with a system user on your server that runs command-line scripts and restarts services, and cronjobs.
Typically what this means is that when it comes time to upgrade Aegir, you not only have to upgrade the frontend site, but also update the components that reside in the 'backend'.
But don't panic! We have instructions and even a script to run, to take care of almost all of it for you, eliminating as much as possible the chance for human error.
2. Upgrade options
There are three options you can choose to upgrade your Aegir install when a new release comes up:
3. New release of Drupal core?
Just as you would use the Migrate task in Aegir to upgrade one of your sites to a new copy of Drupal core, you can follow the UPGRADE.txt to upgrade your actual Aegir frontend system to a new copy of Drupal core too. The upgrade process (including the script) will always fetch the latest available copy of Drupal core to place the frontend on.
Currently you cannot upgrade the Aegir site itself from the frontend with a Migrate task as you do for your managed sites. This may change in the future, but has not been developed yet.