Call multiple AS 3.0 document in a single fla

hi guys,
I am in trouble again.
Is there any way to use multiple document class inside same fla file,
or change document class name dynamically
i have 4-5 actionscript 3.0 file,these 4-5 files have codes of a game say level 1, level 2 ,level 3 , level 4 & 5 entirely different from each other.What i need is that when one level finishes, another level document class should be called?
Any ideas or help…