What should I know before switching my dog to a grain-free food?

Question by Not what you want to hear: What should I know before switching my dog to a grain-free food?
My dog currently eats Blue Buffalo (and loves it), but I think she might have a grain allergy, so I'm switching her to a grain-free food. I'm going to switch her over to Wellness Core.

I just wanted to know how long I should take to switch her over; is two weeks enough, or could it be done in less time? Any other advice from those who feed their dogs grain-free?

Thanks for your

Rice Cereal for Infants