Hello, and sorry you're having problems.
The issue is- you cannot change your CC info directly on the Kindle. This is done for security.
To change any CC information, you need to update your Amazon "One Click Payments" credit or debit card info from a PC (not from the Kindle directly) at the link below:
Feel free to reply back if you need more help, or want to reply back with more details. It does not cost you anything more to reply back once you've rated. Please do rate me positively (at least 3 STARS) and I will continue with you until this is sorted. The positive rating ensures I am credited for my work.
Do you need further assistance with this?