As doctor have say low fat diet is not healthy does that mean I replace low fat milk with whole milk and eat butter and whole fat cheese?

Low Fat Diet. No i think your doctor did not mean to consume fatty foods but to eat a balanced diet, not one specifically trying to eliminate fats as some fats, like omega-3's are essential fatty acids and quite beneficial to consume. Focus on a plant based diet and learn more about the mediterranean diet as it is regarded as one of most balanced, healthy diets that limits many diseases from developing.