On the subscription page you can find the current plan, the total amount of used interactions, seats and bots. You can see your invoices or change your payment methods by clicking on the 'Manage payment method & view invoices' button as depicted below. After clicking a new tab opens your personal customer portal.
Should you wish to upgrade or downgrade your plan, you can decide to do so at any time. The effective changes are immediately implemented. Please be aware that downgrading is immediate, but you are charged for the initial plan for the remainder of the month. Each plan comes with an included number of interactions per month, included number of available bots and an included number of available developer seats. For some plans it is possible to increase the included number of interactions, bots or seats against an extra monthly fee on top of the indicated monthly subscription.