change credit card

Go to the my T-Mobile app. Tap on the bottom on the bill tab. Tap on make a payment. Tap on ADD card.

After you add a new card you should be able to delete the old card.

I had to call Customer Care to get mine changed.  I am not sure if they have fixed whatever was preventing me from doing so online in my account, but Customer Care got it done in a couple of minutes. 

Stored payment methods self-service

Customers can choose to store their bank account or credit/debit card information, one of each, for a total of two stored methods, when making a payment. Only a PAH or Full user will be able to add/edit/remove/use stored payments at My T-Mobile.

Set up a stored payment method

1. Go to My T-Mobile and log in to your account.
2. Select Make a payment.
3. Click Payment Method.
4. Select Add Card or Add Bank.
5. Enter Card or Bank information.
6. Verify Save Payment Method is checked.
7. Select Continue.
8. Select Agree and Submit to complete payment. The stored payment method is now saved for future use on your account.

Update stored payment method

1. Go to My T-Mobile and log in to your account.
2. Select Make a payment.
3. Click Payment Method.
4. Click Trash Can to delete existing payment method.
5. Click Yes to remove the payment method.
6. Click Continue.
7. Click Payment Method.
8. Select Add Card or Add Bank.
9. Enter Card or Bank information.
10. Verify Save Payment Method is checked.
11. Select Continue.
12. Select Agree and Submit to complete payment. The updated stored payment method is now saved for future use on your account.