Pleaser light-up shoes

Hi I bought the Please light-up shoes ( really cute shoes btw) and I pulled the yellow tabs out to activate the lights and one of the shoes flashed for a second and doesn't work anymore. I want to change the battery to see if that's the problem but I'm not sure how to do it. I took out the lights from the heel like it said and there are two circles, one on top of the other( one is obviously the battery) but I don't know how to get it apart and I don't want to break it. So does anyone know about it or had this type of problem before? Thanks, Sable