Design And Develop Modern Website With Latest Technologies

I will follow below steps to do TYPO3 upgrade

1) Backup all files / db
2) Start upgrading TYPO3 core LTS TO LTS
3) Do fixing or migration of TYPO3 Core Content Element.
4) Start upgrading custom extension.
5) Do fixing or migration of TYPO3 Custom extension.
6) Start A/B testing.

Best Regards,
JIMIT SHAH