actionscript 3 - How should I manage game levels in a flash games?

I am still learning and I am trying to design the game levels for my first game (a platformer).

I have some straightforward questions because I feel I am on the wrong way.

Should each level have its own class ?

The way I am trying to do this is, when one finishes the first level I set all variables to null that belong to that class, unregister all events and remove all children from the stage, call a second level constructor, without declaring any variable, new level2(); and set a static var to true "in order to save" that progress in case one wants to play that level again.

However I see the code becomes messy, I run into issues, and memory management concerns arise.

I searched for help all over the internet but I can't find any tutorial that explain it in details, so I'm trying out many ways of achieving what I want, but now I am really in need of some advices to not get lost.