Using "Classes"

I created 'Classes' for the first time in 2016.
Those students have now moved up a grade.

1. Can they still log in with their usernames from last year?
2. If I delete a class, what happens to those user accounts? Can they still login?
3. Those students are now in different class configurations. Can I move students between existing classes?
4. Can I rename the classes?
5. Can I hand the 'Class' off to another teacher?

Thanks