stop baby from breastfeeding

any advices to practice my 1yr and 10mos old son from breastfeeding since we're expecting a new baby, 4mos preggy now. planning to stop it when he reached 2yrs old but i want to start practicing him using bottle. he's been exclusively bf, paminsan minsan nagfoformula siya pero di pa talaga sanay... hindi iniinom paminsan. thank you.