How do I cancel my Credit Card on Itunes?

I canceled my credit card and now i want to buy apps from the store by my redeemed codes. I have $10.00 on the account but when i go to buy an app it sends me to my old billing information. how do i cancel the card and switch my plan to no credit card? when i click view my account it goes to my billing information. Please no opinions. and please if u know help.