What do I do if I want to wean my baby off of formula?

Gradually or at once. After a baby is 12 months of age, and is eating a variety of baby foods, he can be weaned off formula and start whole cow milk. The weaning can be gradual over a week, in which more and more cow milk is mixed into the liquid formula each day. By the end of the week, the baby's drink will be mostly or all cow milk. Or one can wean suddenly, by making the formula disappear and just offering milk.
Transition. When weaning off formula, mix current formula with cow's milk (or whatever milk you will change to) 3/4:1/4. After a few days, decrease formula to 1/2, then again to 1/4. That will minimize risk for GI upset, or for the baby to reject the new milk.