It is very important to keep your Qubes OS system up-to-date to ensure you have the latest [security] updates, as well as the latest non-security enhancements and bug fixes.
By default, the Qubes Update tool will appear as an icon in the Notification Area when updates are available, but you can also start the tool manually by selecting it in the Applications Menu under "System Tools."
Even if no updates have been detected, you can use this tool to check for updates manually at any time by selecting "Enable updates for qubes without known available updates," then selecting all desired items from the list and clicking "Next."
As an alterntaive to the Qubes Update tool, advanced users can update each of the three types of VMs manually.
Visit the pages linked above for details about updating each type.
For example, you might be using a [Fedora TemplateVM].
The [Fedora Project] is independent of the Qubes OS Project.
They set their own [schedule] for when each Fedora release reaches [end-of-life] (EOL).
You can always find out when an operating system reaches EOL from the upstream project that maintains it, but we also make EOL [announcements] and publish guides for official TemplateVM operating systems as a convenience to Qubes users.
When this happens, you should make sure to follow the guide to upgrade to a supported version of that operating system (see the [Fedora upgrade guides] and the [Debian upgrade guides]).
The one exception is dom0, which [doesn't have to be upgraded][dom0-eol].
