LOL, stop eating garbage, make a real effort to exercise. Here is a list of things you can do to help you out (some things may apply and others won't, doesn't matter)
-Don't eat MacDonalds
-Join a gym or take up a sport such as karate
-Perhaps become more physically active in your daily life
-Drink 8 glasses of water a day
-Don't drink sugary drinks e.g. Coke, only drinks with natural sugar such as juice
-Don't eat sugary foods such as cakes and candybars, fruits are a health alternative
Here is the food pyramid, study it and let it be your guide for nutrition.
If all else fails motivate yourself by wanted to change yourself. I mean after all if you are fat, do you wanna stay fat for the rest of your life?