Milk mix is really meant for puppies that are under 8 weeks of age that can't eat solid food yet. Shera is old enough now to eat solid food. Shera's weight of 4.5kg is a little over 9 pounds which is okay for a 2 month old. I would follow the feeding instructions on the back of the Royal Canin puppy food package for his age. Don't worry, he will continue put on weight as he grows. A grown male German Shepard should be around 65-75 pounds.
I hope this helps and thanks for using Petco Pet Education Center, formerly Petcoach!