To upgrade to WP Simple Pay Pro from the Lite version, you’ll first need to purchase the license best for your needs.
Next, click on Plugins → Installed Plugins, find WP Simple Pay Lite, then click Deactivate.
Now scroll back down and click Delete on the deactivated plugin. You’ll be asked to confirm the deletion as well.
Note: Your existing forms and settings will not be deleted.
Now you’re all set to install WP Simple Pay Pro!