How can I lose 20lbs?

I want to lose 10lbs to 15lbs by my bday next month. I'm not going to be shy, I'll admit I'm a girl, 19 almost 20yrs old, 5'3" and right now I'm 173lbs and I want to get to 163lbs..and I hope by August I can be 155lbs to 150lbs. I really want to lose weight, and I know my weight for my height isn't healthy right now and that's one of the main reasons I want to lose weight is to be healthier and look better. I went vegetarian 3yrs ago and went from 190lbs to 170lbs, but I would love to lose an extra 20lbs to 30lbs. Some advice would be greatly appreciated, thanks..ooh and if you wanna be rude it's okay :)