Unload child movie on enter frame

I have a problem.
I am attempting to build a site using load movie commands.
I have a navigation movie with 4 buttons, on the press of each button I uesd this script.

on (release) {
_root.bckGrnd.loadMovie(“NewsLine.swf”);
}

this loads an animation and plays into the news reader.

on the press of a button to go back I have loaded a seperate back animation using this script

on (release) {
_root.bckGrnd.loadMovie(“NewsBack.swf”);
}

The problem I now have is I want to remove this clip at the end of the animation and return to the root navigation.
Does any one have any tips/links on how to do this? or if there is a better way Please help!

Thanks