Your payment details are handled by Stripe, our payment provider, not stored in Mailsuite. That's why there's no option to remove your card from your dashboard: you can replace it with another card or with PayPal.
Replace your card
1) In your dashboard, click the gear icon at the top right to open Settings & account.
2) Click Subscription and then Update payment method.
3) You'll go to a secure Stripe page. Choose Card or PayPal, enter your new payment details and click Save.
Stop future charges
If you don't want to be charged again, cancel your subscription's automatic renewal. Your plan will stay active until the end of the current billing period.