how do i make it so i dont have a credit card set up to my computer

i used to have my moms credit card set up to my account but now i dont want it on there and i want to make it so it has no credit card and only pays off of itunes cards.. i dont have any itunes cards at the moment though and the only other way i know of doing this is by making a whole new account and saying i dont have a credit card and i really do not want to do that because of everything i have done with this account.