I would still say if you want to transition your puppy to adult food that you need to do it gradually. Any sudden change can and usually will upset their sensitive digestive systems. Good luck!
I thought I'd leave this link:
Small Breed Puppy Nutrition
Small breed puppies have higher metabolic rates per pound than larger breeds. Small breed puppies need more protein, fat, phosphorous and calcium to support bone and muscle development. Because small breed puppies like Yorkies also have smaller mouths and smaller stomachs, they require kibble that is easy for them to consume in order to get the nutrients they need. Small breeds also reach mature weight faster than larger breeds, so gradually transitioning to adult food after one year is recommended.
Read more: Dog Food for a Yorkie Puppy | eHow.com
Dog Food for a Yorkie Puppy | eHow.com