Before you start updating or upgrading your Drupal installation, it is important that you know the difference between a major and a minor version release.
- A major version of Drupal core is represented by the number before the first decimal. For example Drupal 6.1, Drupal 7.1, and Drupal 8.1 are all different major releases. This is considered an upgrade.
- A minor version of Drupal core is represented by the decimal. For example, Drupal 7.1, 7.13, and 7.23 are all different minor releases of Drupal 7. This is considered an update.
Major releases include changes to core and how Drupal functions. New tools, structure changes, how everything works and looks, can be changed in a major version update.
Minor releases fix security issues and newly discovered bugs but include no new features.
Drupal Minor update procedure
With a minor release update; such as from Drupal 8.0 to the latest Drupal 8.x version, you do not have to apply all the updates that have been released between the versions. You can jump directly from 8.0 to that version.
Drupal Major upgrade procedure
A major release upgrade requires you to first update to the current minor release prior to applying the major release update. If 7.19 is the current version of Drupal 7, and your site is running 7.13, you would first need to update to 7.19 and then apply the update to the current major version 8.
You cannot skip major releases when upgrading your site. This means that if you want to upgrade a Drupal 6 installation to Drupal 8, you must first upgrade from Drupal 6 to 7, and then up to Drupal 8.
However, if you have a complex Drupal 6 site that you would like to upgrade to Drupal 8, you may want to consider starting the code and configuration fresh in a new Drupal 8 installation, then importing content and users from Drupal 6 using Migrate or similar modules.