How to upgrade from 2.0.3.1 to 2.1.0.1?

Hi!

Is there any known guide how to upgrade version 2.0.3.1 to 2.1.0.1?

Also how big changes there has been made on 2.1.0.1 when comparing to 2.0.3.1? Should same themes and extensions work on both of them?

ps. I have read changelog but that doesn't say much to me...

There is a text document included that explains on how to upgrade, just make sure you have a proper backup of your files and database for in case things go wrong. Or do a trial first on your local machine.