Hi Suzieb,
Jake has Millies and loves it,and it is a good quality kibble.
I would ring the company and ask for their advice.
They were really helpful and not at all pushy when I rang them about Jake's diet ( he had been loosing weight and had runny poo when he was on Eden)
However most of the advice on this site is not to change food straight away, it will be a big enough change for your little one leaving his mum and litter mates and settling in a new home without changing his food straight away, especially if he is doing well on it and enjoys it.
They can often go off their food when they first arrive in their new home.
Jake loves food, all food but when he first came to live with us he didn't eat that afternoon and evening. ( but some puppies take longer)
His breeder had warned us that this can sometimes happen so I tried not to worry too much, he had a drink so that was good, next day he gobbled all his food down and has been a lovely food monster ever since!!
Have fun with your puppy, they grow up so quickly