You can change your plan through your billing settings here. From there, you can upgrade to Pro or downgrade to Starter, and your billing will adjust accordingly.
Changes are prorated, so you're only charged for what you use, if you upgrade mid-cycle you'll pay the difference for the remainder of the period, and if you downgrade, the adjustment is reflected in your billing.
If you have any questions about which plan is right for you, or need a hand making the switch, reach out to the team at [email protected] and we can help you find a plan that's the right fit.