TYPO3 v6 has reached its end-of-life April 18th, 2017 and is not maintained by the community anymore. Looking for a stable version? Use the version switch on the top left.

There is no further ELTS support. It is strongly recommended updating your project.

Check the ChangeLog and

Look through the ChangeLog and the files in your extracted TYPO3 package. They contain information about new functions you might need or be interested in.

Especially pay attention to lines starting with "!!!". They are especially important, because they are about changes that may affect the operation of some websites.