That method of updating now only applies to the Enterprise (Business) products. The consumer version updates by engine in a totally different manner and can't be updated manually without an Internet connection.
One of the system requirements of the consumer products is an Internet connection.
Is there a method to downgrade to the previous version? because with the previous version it was possible to update dat file this way.
No there isn't sorry. If you purchased the update to the new version you can obtain a refund through Customer Service, linked under Useful Links at the top of this page.