We started to replace one bottle a day at 11 months (with the rest being formula), then another at 11.5 months and then switched completely on her birthday. She occasionally had some cow's milk as a drink with a snack around 10.5 months though, but not in place of formula at that point. You do exactly the same as you would for formula, feed on demand at the same times she'd normally have a bottle or cup of formula.