Thank you. So is ND designed to be used on its own or with dry food as well?

I've asked Arden grange for a sample which they are sending but now I see their puppy food has maize (as per my other post!). It is soooo confusing!

How would I change over a puppy from the current breeder's dry food to ND? SHould I keep feeding it for a week or so and then gradually add ND to it and lessen the dry until it is all ND?