We went from EBM (via bottle), and we had to do a bit of a gradual transition - she didn't like the taste of cow's milk. Pie was about 13 months when we started shifting to cow's milk & just over 14 months when we changed completely. I did it by mixing a bit of cow's milk in with her EBM and gradually upping the amount of cow's milk. You can do the same thing with formula, just mix up a smaller amount (but in the same ratio of powder to water) and add a bit of cow's milk in.
Or if he doesn't mind the taste, try switching one or two bottles a day over.
Four or five a day does seem like a lot of bottles at 12 months, but if he's eating well I can't see the harm in it...Pie was probably having the same at that age although hers were mostly overnight, and she still has bottles now (she has just turned two).
Do what suits you & your LO