How to kill entity node?

In my program i want to destroy-unload entity and node. In my game its just killed and i wanted to free some ram. How to do it ? makin node and entity to null or disposing them dont work. Er mayby it works .. but all the subclasses stay as name or other :/ then i cant recreate again new object for excample with the same name :/. tried to remove name but this function dont react.

scenemanager.DestroyEntity();
scenemanager.DestroySceneNode();

to force garbage collection:
GC.Collect();

I don't know too much about garbage collection though