After purchasing the Pro version you will receive a welcome email. If you can’t find it in your Inbox check the spam folder.
In that email you will receive a link to the Pro version that you need to download. You will also receive info about the license code that will be needed later.
After downloading the Pro version go to the WordPress admin Plugins page and deactivate the Free version of WP Mobile Menu. Then you can install the Pro version using the zip file downloaded from the email.
Ok, you have installed the Pro version now hit the activate button.
The settings from the Free Version will move to the Pro version. Now you just need to configure the additional settings of the Pro version.