Formula feeding advise please for 12+ months

Ra

My little boy isn’t tolerating cows milk well. We’ve tried to wean a few times from formula to cows milk with no success. He’s fine with it in food and cereal but not to drink

He’s on cow and gate stage 1 formula. I know I should probably move him to stage 2 or even 3 for his age now. He’s 13 months now. Should I change to stage 3 from 1? Or stay at 1.