You should do a slow switch from whatever your breeder had the pup on to avoid upsetting the stomach to much if it's necessary. Different breed's have different requirement's so you should talk to them about that as well (they should know the answer's) and then find a five or six star rated food on the analysis site that fit's (if the food your pup is already on doesn't match) and you can get. Your breed club also likely has some very useful information.
www.dogfoodanalysis.com
www.dogfoodanalysis.com
