Before even changing your diet, monitor how you eat now. If you have trouble keeping track in your head, write little notes or make a journal somewhere.
Also, changing you diet isn't a temporary thing. If you go back to your old diet, you'll go back to your old body unless you're doing something else to balance it out, like more exercise.

I cut as much fat out of my diet as possible for a galbladder condition, and was pleasantly surprised how many no-fat/low-fat items are out there. I even found fat free cheese slices! I made my own meals and kept a food diary for awhile, but the diary died after a month, which shows some new habits take more work to establish than others. ^^;

I've been told that portions is the best way to help in losing weight. Monitoring what you usually eat, cut back on sugar products, and don't just eat till you feel you're about to burst. Some people have the problem of eating when bored if you have this problem please try to preoccupy your time :3 Hope this information helps some =^w^= mew!

Start exercising. The diet alone won't do much.

My fitness pal. I'm using in in my nutrition class and it really helps. Also try watching Supersize me... you'll change your diet after seeing it.