Mommies, how do you switch from formula to formula? From the very begi…

Mommies, how do you switch from formula to formula? From the very beginning I notice that the formula doesn't suit me (even though it's not cheap), the stool is irregular and green, colic hurts terribly, even though we give simethicone, eats reluctantly. By the way, half of it can be thrown up. I ask the pediatrician, she says that I'm overdoing it and it's adaptation of the intestines. I understand everything, but how long can this go on... The baby is always worried about throwing up too much and getting hungry. How can we switch, can we do it immediately or gradually?