First, drop sugar like a bad habit. No soft drinks at all, candy or anything like that. Muffins from Starbucks, hot chocolate, cookies, cake, etc. That alone should make a huge difference.
If you've got that under wraps (meaning 90% of what you eat isn't processed sugar), do some weight training. The more muscle you have on your body, the more fat it burns. Two or three one hour sessions a week. Can even just be body weight: pushups, squats, lunges, step ups, crunches, etc.
Lastly, do some intervals a couple of times a week if you can. I.e. Sprint for 1 minute, take a 1 minute break and repeat, 10 times. Variants on that will help. You can race up stairs or do rows instead (basically any exercise). And do different times: 2 minutes of work, 2 rest or 3 on, 1 off. Basically do intervals for 12 - 20 minutes.
It'll take awhile, but if you do two out of the above three suggestions, you should see changes in a few weeks.