I was encouraged to switch one bottle every two days, to the second stage milk, this was so that you could monitor any reaction, or upset tum from the stronger mix. Hope this helps, best wishes.

Luv Winnie.xxxx

If you feel your bubs needs the more satisfying milk, then he must have it.  As for how to go about it, the 1/2 and 1/2 method is probably the best way to go so he can get used to the taste.