How do you change the battery on a light-up pacifier necklace?

It's one of these: http://coastentertainment.stores.yahoo.net/pacifier.html



More specifically, how should I go about opening up the back to change the battery?How do you change the battery on a light-up pacifier necklace?
You some how open if you cant then that mean you cant change it without damaging it

I have 2 , white and blue.