Overweight need help !

S • 18.
I'm 17 and I'm short 4'11 I'm overweight. I'm about 180-190 idk the exact weight. I want to lose weight but idk how I don't eat junk food or candy and I don't drink soda. I actually drink a lot of water. And I don't eat a lot. Last year i was losing weight without even trying I didn't change anything and now ever since 2014 started I've been gaining it all back. I really want to be at least 140 by next summer or even less. Please help !