Best Ways To Lose Belly Fat How To Lose Belly Fat Fast

The quickest, free way to lose belly fat?
I know spot reduction doesn't work now, and the best way to burn fat is by doing cardio exercise 4-5 times a week. How do I do this quickly and efficiently; enough to show a change by valentines day?
If it helps, I'm a 17-year old female, slow metabolism, and I don't eat much, maybe 2 meals a day, no fast food, mainly home-cooked meals or pizza lunchables (strange addiction).
Please no ads about products or anything. I don't have the money or credit cards to pay online for something that could just as well be a scam. I'd rather do this the normal way, even if it's slower.
Sit-ups! Drink plenty of water! Walk about a half mile per day. Good Luck