WP Smush Plugin will not upgrade to Pro version

I have tried several times to upgrade my WP Smush Plugin to the Pro version, but is only the standard version. I have deleted the plugin and installed via the Dashboard and it still reports the I can have the standard version. I have also deactivated all my other plugins and re-installed the WP Smush plugin with no change. Is there another way to upgrade the plugin to the full Pro version?