how to to lose 20 lbs in 3 to 4 months?

[luckycharms]

I'm 5'3" and 155lbs. My measurements are chest:39", waist: 35", hips: 39", thighs: 24", and arms: 13". How should I eat and what kind of workout routine should I do to go down to 135? I'm 21 and I'm tired of being fat! I feel like it's impossible to shrink my waist to a 25!