Wow, that’s an old one!
Please upgrade to the newest version (preferably 2.5.6), available at your account page. You will have to do it manually (deactivate + uninstall current version, then install + activate new version).
After installation enter your licence key at Settings > WooCommerce Extended Coupon Features to enable automatic updates.
PS: You can remove the free version of the plugin, you don’t need it when you have PRO installed.