I agree with the advice to gradually blend in cow's milk to the formula your child is used to. Of course, there's always the way my mom used: the first bite, we got weaned, and if we had any objections to cow's milk, we simply got offered nothing else until we were hungry enough to take it!
But this IS a nutrition group. Given a choice, I'd never switch a child to cow's milk until they were taking several solid foods to balance the change in nutrition.