Development 

The following steps should help when you find yourself in the position of having to update an existing extension for a new major release of TYPO3. Before you start, make sure you know whether the upgraded extension needs to support more than one major release of the software.

1. Use TYPO3 Rector on the extension's code to get an idea of what needs to be changed. Rector can automatically implement a lot of necessary changes for you and will tell you about other things you need to change by hand.
2. When this is done, switch to a development environment updated according to the TYPO3 release's changed requirements. Use the updated system's integrated extension testing tools to see which further changes are required.
3. If you make changes that affect the database, make sure there is an automatic upgrade script in place.
4. Check that the extension is working as expected. This can be done manually or with the help of an automated testing pipeline.
5. Edit the metadata to increase the version numbers of both the extension and TYPO3. Add the changes to the changelog so other developers can see what changes were made when they use the extension.