H.L.
You would switch the same way you will wean him off of formula when he is older. Just be careful if you switch to the good start, you might want to stay there, if you keep switching back and forth, his little digestive system will get very confused and cause painful gas and constipation (happened to my nephew) When I switched my daughter (now 8) from Similac to Good Start, I replaced 2 oz of Similac with Good Start for 4 days at a time. She handled the change wonderfully. Good Luck!!!