You can change your payment method through your account: Account → Rate Plan → Subscription Management — Add a new payment method
Alternatively, use this link to change your payment method directly: https://{{host}}/dashboard/payment/portal
No credit card is required. You can upgrade at the end of the trial or continue using the Free plan.
Go to: Account → Rate Plan → Subscription Management → Cancel Subscription
Alternatively, you can use this link: https://{{host}}/panel/account/payment