To upgrade your subscription, head to Settings → Billing → click on Manage plan. This will open a new tab where you can update your subscription plan.
In the new tab, select Change Subscription and choose the plan of your choice. This will redirect you to the checkout page, where you can see the payment details and add potential discount codes before Confirming.
Please remember to toggle the monthly/annual tab to ensure you choose your preferred billing method.
I hope this helped!