Changing formulae milk

Hi mummies, I’m currently feeding my baby S26 Gold FM but I’m considering to change it to NAN optipro FM. Do I just change the milk powder and introduce her like that? Or do I need to mix the powder cos I’ve seen some articles claiming that I should mix both powder? Is it even ok to mix 2 different brands?? #advicepls #firsttimemom #FTM #Needadvice #firstbaby