The posters above have given technically good advice, but failed to mention what approach you should take.
If you try and cut out sugar, dairy, fruit, fat, etc. all at once, you're setting yourself up to fail.
The first thing you should do is keep track of your eating habits for a week. Don't try and alter them at this point, simply record. Be as detailed as you possibly can - the amount you eat/drink, at what time, where, how you feel (hungry, sad, angry, etc.) when you're eating, or anything else you feel is relevant.
After doing that, you can identify areas to start improving. For example, if you find that you are drinking 4 glasses of Pepsi a day, try cutting that in half over the period of a week by slowly reducing how much you drink. If that is successful, cut it in half again. Try replacing the Pepsi with something lower in sugar to start, or if you feel able, something calorie-free like water or tea.
If you find that you always succumb to a craving or have the need to binge right when you get home from work, then try bringing a snack with you to work, and instead of going right home, go to a park or something, eat your snack, and then go home.
To reiterate, the trick is to make small changes that you can stick to, track your progress, and if you slip, then to just get back on the horse.