Ay, ganyan din ginawa namin with my eldest kaya alam ko yan! Best way is to do it gradually, mix the old milk with the new one for about a week or two, slowly increasing the ratio ng Nido until pure Nido na, that way hindi mabigla ang tummy niya. Sa pagtimpla, usually 1:1 talaga (one scoop to one ounce of water or follow the tin's instructions), pero check mo muna ang exact ratio sa Nido box para sigurado. A few of us moms also noticed na sometimes babies get a bit constipated during the switch, so observe her poop for a few days; if worried, best to ask her pedia para ma-guide ka ng tama, lalo na since she's been on the same milk since birth. Good luck sa transition!