Yup, in the code where you decrease the life variable by one, use this code:

Actionscript Code:
unloadMovie(_root["heart"+life_var]);

Suppose life_var is the variable for the lives, and you have 10 hearts, each with their own instance name, like heart1, heart2, etc. _root[] will find movieclip, variable, or anything else which has the name of the parts inside the square brackets put together. Let's say life_var is equals to 5, meaning that we've lost five lives. Then, when losing another life, life_var will be decreased by one, making it equals to 4, and then the movieclip which will be unloaded, will be, _root["heart"+life_var], which now would make up, heart4 - so the movieclip with the instance name, heart4, will be unloaded, aka, deleted. This is to prevent you from writing 10 alike codes, just to remove each individual heart. If you don't understand, just say so, and I'll make you an example

and No problem