Destroying instances

I have a class that displays a picture in a popup style.

var popPicture:PopPicture = new PopPicture

To remove it I use


and to remove completely the instance I pass


But doing debugging I have discovered that I can trace the name of the instance using

and every time I create a new instance of the popup, the name is increased instance25, instance27, instance28.

I am not sure if it is just an internal counter that do no reuse numbers o if the instances are not really deleted. Can someone tell me if this is the ritght way to delete instances?