I want to loose 8-10 kgs (22 pounds). What is the healthiest way for it and to prevent it from comming back?

I am 5'4 and weigh 57kgs (127 pounds). I want to become slim and become about 48-49 kgs. What is the best way to loose the weight and prevent it from coming back? I want to loose this weight in 3-4 months. Which exercises are the best? Am I fat currently?