I don't have very good will power with food either. I've always pretty much eaten what I wanted and could get away with it because i was really active, but that is changing...
What I do is try to stick by the rule of one-a-day, meaning I get to have one unhealthy/junk item per day, and that's it - everything else has to be healthy. (that means one regular kind of serving, not like a whole gallon of ice cream! :)
I basically don't buy junk food, or if I do, just one thing at a time - if it's not in the house, it's a lot easier not to eat it!! If you have stuff you know is bad, you might just do a cupboard cleanup and literally throw or give away the bad stuff. Try to buy the simplest, freshest, un-processed foods you can - no premade entrees, for example, because those are loaded with fat, sugar, salt, refined sugars and flours, corn syrup, etc -- generally not good nutrition. Buy things you like to eat that are healthy. Forget about anything fried altogether. If you like fresh fruit, fresh veggies, now that everything is in season, it's a great time to start. I find that in the summer, I pretty much want to live on salads, pasta, corn on the cob, and occasionally grill something.
The other thing I do is walk every day. As fast as I can for a half hour or so, or longer if I can get the time. (Jogging is better, and with that, I motivate myself by saying 'just 10 minutes' - the key is getting me out the door, and sometimes I go longer... I'm struggling with a bad knee). Even walking really helps - if you can go walking, or better yet jog, it really helps me to slim down.
Good luck... just take small steps, maybe one new step a week. You'll get there!