Hi Becky,
We switched from bottle of formula to sippy cup of water during the day first (around 10 months i think...) Once soldis were fully established, we offered them first, with a cup of water, then milk afterwards. She started to drink less and less, then refused the milk altogether.
The formula in the morning was replaced with cows milk a around 1 year and put into one of her suppy cups. We got lucky wth the bedtime bottle as she had a tummy bug and refused it 3 nights running, so we switched that for a cup of milk too (15 months)
HTH
H