Since version 1.7, the updating and upgrading of Joomla are built into the administration interface as a component. For example, version 3.9.5 is Joomla major version 3, minor 9, and maintenance release 5. Joomla is released with the following version designations.
If you are already confused or don't know what a major version is, you should read more about the release and support cycle of Joomla CMS Versions. This is especially true if you are changing to a major version.
Before you begin, it is essential you know what version of Joomla! you are using.