Options for updating Drupal core
Overview of your options to choose from to update Drupal core
Updating Drupal core via Composer
Update Drupal core using Composer, the PHP dependency manager.
Updating Drupal core manually
Update Drupal core using a manual installation from the UI and command line.
Updating Drupal core via Drush
Update Drupal core using Drush, the Drupal Shell.
Updating Modules and Themes using Composer
Updating Drupal modules and themes using Composer.
Migrating the Composer project for Drupal earlier than 8.8.0
Troubleshooting guide for moving from the community-contributed Composer template to the official template.
Troubleshooting database updates
Troubleshooting steps to take if update.php reports a problem.
Known database update issues and workarounds
Known database update issues and workarounds
Responding to critical security update advisories
As of Drupal 9.3.0, highly critical security advisories will be displayed on Drupal administration pages.
Automatic Updates
Drupal 8 documentation of the how and why of automatic updates.
Deploying a Drupal update
Details the process of deploying a Drupal update to a server, and of new features