If you want to upgrade from Pro to Business+, or downgrade please do the following.
To update your subscription or change the plan that you’re in click on the Billing page in the web app. This will load the Stripe billing portal. For example if we want to change from monthly to yearly we can do the following:
We click on update subscription button then on the on the Yearly tab. Here we select either the Pro plan or Business Plus, and then we click continue. On the next page we click subscribe and pay.
See demo below.