Question about "destroy"

How would you guys make all the actors destroy upon level completion ? Im currently having my game images go up to 80 MB because Im pretty sure it has to do with all images being stored up on memory and not being destroyed upon level completion.
Comments
All the actors that I want to be destroyed have a rule behaviour that says 'when level_ended=true destroy actor'.
If there's a better way, or if this unnecessary then I'd be interested to know.
Simon