Classic mode upgrade 

Minor Upgrades - Using The Core Updater 

The "Install Tool" in the section "Important Actions" provides a function to update the TYPO3 Core.

In the section "Important Actions" scroll down to "Core update" and click the "Check for core updates" button. If the requirements are met, TYPO3 will automatically install the new source code.

Database updates are usually not necessary, though you still have to remove the temporary cache files. After that your update is finished.

Major Upgrades - Symlink The Core 

Go to https://typo3.org/download/ and download the source package of the new TYPO3 version.

Extract the package on your web server and, in your TYPO3 document root, adjust the typo3_src symlink.

Make sure to upload the whole TYPO3 source directory including the vendor directory, otherwise you will miss important dependency updates.

Make sure to read the release notes of even the minor versions carefully. While great care is taken to keep the minor updates as easy as possible, (especially when releasing security updates) more steps might be necessary.

In case of a major update, e.g. from TYPO3 11.5 to 12.4, go ahead with the next step!

Also check out any breaking changes listed in the changelog for the new version.

Disabling the Core Updater in a classic mode installation 

The Core Updater functionality can be turned off, in order to avoid users using it, i.e. if you use your own update mechanism.

This feature is already disabled when TYPO3 is installed via Composer.

To disable the Core updater, you can set this environment variable:

TYPO3_DISABLE_CORE_UPDATER=1

SetEnv TYPO3_DISABLE_CORE_UPDATER 1

server {
  location ~ path/to/it {
    include fastcgi_params;
    fastcgi_param TYPO3_DISABLE_CORE_UPDATER "1";
  }
}

This will remove the button and all related functionality in the Install Tool.