Anyone know anything about switching infant formula?

ok i know that it has to be a gradual process when switching for example from soy formula to milk based formula..

but i was just wondering if it has to be the same if im switching formula's but both are milk based? my pediatrician said if im going from soy to milk based, to do it gradually.. (just like you'd do dog food switching)..

but since im going from a milk based to another milk base formula (just different brands).. do i still have to do it gradually

i wish i could call my pediatrician, but he's not on duty on sundays.. and i dont think it's appropriate of me to call the emergencyroom to ask such a dumb question lol.. can anyone tell me asap?

cause i'd like to switch to this brand asap, if at all possible