Yeah, start off by just adding a small amount into the existing food and and you can gradually reduce the amount of old food you give until you give just the new food.
I did this when changing from museli to just pellets, i did it over several weeks so i used the rest of the museli bag, ny girls now have harringtons and burgess excel pellets the latter of which were introduced over about a week, initially i mixed it in the same bowl but now i have it separate and they just choose what they want to eat.