How to loose fat while maintaing muscle m?what diet is required?

guys i m overweight , i m 21 , 5'6 ,i m 70 kgs(154 lbs). i want to loose my weight and fat , so please tell me friends what diet is required there, but i don't want to loose my muscle m( bit loss is ok, but not more)?? i have seen bodybuilders with just 60 kgs with incredible muscularity. why i m not getting muscles instead of it my weight is gaining. presently i have cutted sugars and fats , i m on weight loss diet with 1870 kcal/day. please anyone guide me regarding weight+ fat loss and muscle gain.