The “Pro” version and “free” version of Instagram Feed are seperate plugins. To upgrade, deactivate and uninstall the “free” version and then use the .zip file that came with your purchase to install the “Pro” version. There is a checkbox on the “Configure” tab to save your settings before you upgrade.
An email should have been sent with the “Pro” version .zip file and a link to directions on how to upgrade. Check your spam folder for this. Otherwise the latest version of the plugin along with instructions on how to install it are always available on your My Account page.