I'm 17 and weigh 67kg and was looking at diets that i could go on and have come across the 'milk diet' but don't know how it actually works.

Eat healthy diet: Any diet that focuses too much on one food, and doesn't give you a good combination of nutrients, is not healthy in the long run. The best thing to do is eat a healthy diet, control your portions and get regular exercise. Fad diets can help you lose weight, but you are very likely to gain the weight back again when you get tired of it.