When a new version of TYPO3 is released, you should follow the guideline in this chapter in order to do an upgrade. Also follow any additional upgrade information carefully. You might e.g. want to skim the Release Notes on get.typo3.org to see if any features affect the way your site works.
Version specific upgrade notes
While this guide is the general guideline to follow for a TYPO3 Upgrade, some version specific information are additionally available in the TYPO3 Wiki. Use them as an amendment to this guide!
Think of active users
Think of users who might want to do any changes during your upgrading and/or fallback. Inform them before you start!
Basically these are the steps to be done to update your TYPO3 site: