Supporters can update their own payment method by logging into their profile, clicking My Payment Methods in the left menu and then choosing to Add a New Payment Method. They can then delete any obsolete payment methods.
NOTE: Supporters will only have the ability to update their payment method through the donor portal if you have enabled the permission to allow them to do so. This permission is found in Settings > Supporter Preferences - Donor Portal Features.
When adding a new payment method, if the supporter has any existing recurring payments, you can choose whether to use the new payment method for them.
If someone on your staff or team needs to add a new payment method for a supporter, you can do so by logging in as the supporter using the Login As feature and adding a new payment method through their profile as a supporter would.
To login as a supporter, go to Supporters in the left menu, find the supporter's profile and click on it to view the profile. Then click the gear icon in the top right and choose Login as...