I'm recently bought Blue Buffalo Small Breed Puppy food for my 3 month old poodle?

My puppy was currently eating Bil-Jac, but I read that it was very bad because it contained corn and chicken by products, etc. so, I switched. I researched this bag, and found it to be quite good. Now I need to know how to transition my puppy from his current dog food to BB. Please and thanks. Oh and the quickest way possible please!