You can change your payment method by going to the Billing section of your Tapfiliate platform. To reach this page, simply click on the bubble on the lower left of your page. 

In the Your next payment section of your Billing page, you'll find the option to change your payment method.

This will open a window where you can submit your new payment method.

It may be the case that you may be unable to submit your payment method, and that the window and input fields look like so:

This is likely due to a caching issue and is very easy to resolve. 

While on this page, hold down Ctrl/Cmd + Shift + R simultaneously. This hard-refresh will clear your cache and open the field, so you can submit your new payment details.