substituting formula

My daughter has always taken 4 8 oz of soy formula since she was 2 month old and lately 5. She eats cereal, fruits, vegetables and pasts daily too. She is not overweight or underweight. The doctor has told me on several occasions that she drinks a lot of formula but never said to cut back and my daughter wouldn't let me anyway. I am thinking of cutting her back to 2 8 oz bottles of formula and 2 8 oz bottles of soymilk. She will still be getting vitamins and minerals from formula and regular food. Does anyone have any comments that could tell me if I should or should not.