Here's how to do this:
1) Find the price you paid for the personal license of the Wordpress plugin
2) Find the current price for the developer's license
3) Send the difference via Paypal to george.katsoudas.payments[at]gmail.com (replace [at] with the @ symbol)
4) Open a support ticket and mention the name of the plugin you are trying to upgrade, as well as your Paypal transaction ID.
We will send you the developer's license ASAP :-)
Article ID: 79