How do you get reduce body weight?

Increase your height or lose weight. Your BMI is a ratio between your weight and your height, the idea being that the normal weight for a short person is much lower than that of a tall person, and that BMI can work across both parameters. Hence if two people were the same weight, but different heights, the taller person would have the lower BMI. In two people of the same height, but different weights, the lighter person would have the lower BMI.

so going to a gym and trying to turn any fatty areas into muscle will lower ur bmi try sit ups push ups and general running cycleing.