I can't get motivated to work out and stop drinking sodas. Help me!?

Well for starters, I'm a 15 year old guy and I'm around 15% body fat. I've been wanting to trim down and build more muscle for a while now but just can't get motivated to stop drinking soda. And it doesn't help that my entire family is overweight and my mom buys 2-4 12-packs of coke a week. Really what I'm asking here is a little help with getting motivated. I already do around 6 hours of cardio a week and eat right everyday (minus the soda).