I have seen soo much great information about what to feed our yorkies but I have yet another question

I have Lilly on Royal Canin, I gradually switched her from science diet ( when I found it its not the best for them) I have noticed she has been very itchy. I have been reading alot about food and am wondering if I should switch yet again? I want to get her on either innova or Chicken soup and am not sure which on is best. Also, is is bad to keep switching like this? Thanks so much for your help