Biggest Loser Time

So, My apartment complex has just started a biggest loser competition. I signed up. I'm incredibly scared. I've always been overweight, well not always but for over half my life. It's attributed to genetics, a metabolism disorder, and plain gluttony and laziness. I've always wanted to lose weight but never had the ambition/will power to. I'm hoping that this will kick my butt! I have to weigh in every friday so I'll try to keep my progress posted! So does anyone have any advice? I don't have a trainer and plan on running. I want to do the chicago half marathon with my family in August! So wish me luck!!