WooCommerce Plugin - Upgrade
You can use the “Upgrade” feature of the KEYZY WooCommerce Plugin to upgrade a license for your customers.
Inserting "Upgrade" Shortcode
With the following KEYZY WooCommerce plugin shortcode, you can display the “Upgrade” form on any page of your website.
How Your Customers Use That Form
They need to be signed in to your WooCommerce store to be able to see the form. They'll see two text boxes. After they enter the serial numbers into the boxes and press the submit button, their upgrade process will finish.