In order to upgrade your free theme to the pro version, you need to go to the premium section of our site and select the Pro theme that corresponds to the free theme you already installed. Once you complete the purchase you will receive an automated email with a download link and a license key for your purchase. You'll need to download and install in WordPress the .zip file for the pro theme to replace the free theme you currently have (make a backup of your current site before in case you run into any issues) and then enter the license key in appearance --> theme license.