How to lose the hump behind my neck I am 55kg and 5'4"tall?

See doctor. Hump behind the neck suggests and endocrine issue and needs to be evaluated by additional history, physical examination and some tests. In the mean time - Have a diet rich in fresh vegetables, fruits, whole grains, low fat milk and milk products, nuts, beans, legumes, lentils and small amounts of lean meats. Avoid saturated fats. Exercise at least 150 minutes/week and increase the intensity of exercise gradually. Do not use tobacco or alcohol in any form.