Transitioning from formula 1 to formula 2 should be done gradually. I read that by mixing in a bit of formula 1 with formula 2 during the first few days of transition will help, baby will be less likely to notice if there has been a change in taste.
For my 3 kids.. I Mix the stage 1 and 2 formula when they reach 6 months old.. After 1 month den fully change to stage 2..
for me after my baby turn 6 month I just the stage one at home then start buying stage 2