Gradual. If weaning from breast milk to formula, pumping and mixing the two in a bottle with a gradual increase in the concentration of formula can be helpful. This gradual approach also works for the transition to cows milk after one year of age.
Around a year, you. Can wean to a cup & avoid the developmental, medical & dental problems associated with ad-lib use of "toddler bottles" & sippy cups. Start by holding a double-handled, open-mouthed cup or "commuter cup" with 2oz. Of formula or water at 9 mos.; give more if still thirsty. D/c the bottles ~12 mos.; limit whole milk & milk products to 16-21 oz./day & juice 0-4 oz./day; & have the 1st dental visit.