Transitioning your companion animal onto a new food can either be tricky or a walk in the park.  It depends largely on your animal.  Generally, for pets transitioning from one kibble to another, we recommend a transition period of 10 to 14 days to start.  This amount of time works well for most, but not all.  Keep an eye on their stools to see if they’re maintaining consistency or not and ease off or continue appropriately.  With the 10-14 day method, we recommend feeding 75% old food with 25% new food for 2-4 days.  Then graduate to 50% old food with 50% new food for 2-4 days.  Then 25% old food with 75% new food.  Watch your animal, they will usually tell you wether or not to slow down.  When they seem ready, you can leave the old food behind.
Transitioning between types of food, like kibble to canned or kibble to raw, we recommend having a conversation with our staff or a veterinarian about your companion animals diet history and health status.  Again, transitioning can be easy, but its best to play it safe and do it right the first time.