Loader class / instance name confusions

I’m creating a site that loads external .swfs as pages. I have little understanding of how Loaders and instance names work with AS3 (even after reading the documentation), so I’m having some difficulties.

I’m loading the .swfs in a movie clip named “container.” I want to replace the contents of “container” with the web page .swf that the user chooses, but I don’t know how to write the condition to:
a) check to see if something is already inside “container”
b) remove the contents by instance name or method of MovieClip. I’d prefer to remove whatever is inside of “container” rather than switching cases for different instances.

Here’s my code:

var container:MovieClip = new MovieClip();

buttonMC.addEventListener(MouseEvent.MOUSE_DOWN, downHandler);

function downHandler(event:MouseEvent) {

function startLoad()
	var mLoader:Loader = new Loader();
	var mRequest:URLRequest = new URLRequest("news.swf");
	mLoader.contentLoaderInfo.addEventListener(Event.COMPLETE, onCompleteHandler);
	mLoader.contentLoaderInfo.addEventListener(ProgressEvent.PROGRESS, onProgressHandler);

function onCompleteHandler(loadEvent:Event)

Thank you.