TYPO3 v9 has reached its end-of-life September 30th, 2021 and is not maintained by the community anymore. Looking for a stable version? Use the version switch on the top left.

You can order Extended Long Term Support (ELTS) here: TYPO3 ELTS.

Check the ChangeLog

Look through the ChangeLog online. The ChangeLog is divided into four sections "Breaking Changes", "Features", "Deprecation" and "Important". Before upgrading you should at least take a look at the sections "Breaking Changes" and "Important" - changes described in those areas might affect your website.

The detailed information contains a section called "Affected Installations" which contains hints whether or not your website is affected by the change.

You can also find the ChangeLog in the Install Tool at "Upgrade Analysis". Here you can mark files as read after checking them, so you get a ToDo list for the upgrade.

Uprade Analysis

The "Upgrade Analysis" in the Install Tool