Q: How do I update my apple id for icloud on my Ipad

I can't sign in to the old Apple id on my phone as it automatically inserts the old id, waiting for the password to be entered. As this id is no longer valid I am unable to access the account on my phone. I can sign in and out on my pc with no problem. Why doesn't my phone get updated to the new id as its the same account?

I can't sign out on my ipad or iphone because my apple id was updated.