Cecile,
In terms of migration from 1.0 to 2.0, you must do this manually. I don't know if I have a recommendation on what to do. I'd say it's easier to start using Forms 2.0 for new things, than try to rebuild each form and update all landing pages for long time users.
That's somewhat unfortunate, but not surprising given the complexity involved. Think of it as a good opportunity to review forms and try things out on the next program. Just being able to do all of this is tremendous.
Marketo instances before Jan 24, 2014 will have access to both types of Forms.