M.P.
I changed my daughter to milk at 11 months. I was giving her formula cold for a while and then did a ratio of milk and formula. For instance in a 6oz bottle do 4oz formula 2oz milk for a couple of days then lower each until it is all milk. This way their tummy dosen't get to upset. I did this for both of my girls and had no issues but both had been drinking the formula cold. I would start for a couple of days w/ just not heating the formula and see how that goes then try to switch.