How to upgrade from Smart to Pro
Go to Site Settings and select 'Upgrade or Renew' and check your current subscription.
Before upgrading from Smart to Pro, you should make sure that there is no auto-renewal subscription on your Smart website. If there is one, you will need to cancel it by logging in to your account on the corresponding payment gateway (iTunes / Google Play / PayPal / PayPro Global).
Once you do not have an active Smart subscription, you will be able to opt to subscribe to a Pro site.