You don't need to restrict yourself 24 hours a day. Don't worry if you have a Big Mac and fries for lunch. Just make sure you balance it by having a nutritious dinner. Moderation is the key. Try having a banana or some yogurt as a snack instead of junk food.
Small changes can lead to a big difference.
I don't have any will power. This is a tough one. You can avoid situations where poor will power will hurt you, such as going out for beers after the game. You can try to eat meals with someone who can support you and won't be a bad influence on you. I can't afford to eat healthy food.