For your customers and resellers to upgrade their O365 trial subscription to a paid one, they must open the subscription in Storefront and select the action "Upgrade to Paid".
This action will redirect the user to the "add to basket" page where your customer or reseller can define how many licenses he wants to purchase. In this page can see also the available add-ons for the service he tried and now wants to purchase.
Then, the user will be redirected to the basket for completing the upgrade.
