Does it show in the list of eCart objects? You may be able to just open the eCart object and click "ok" to update it. You would still likely want to go through and update the view cart and checkout pages to use the latest version, but it might not be necessary. I know it would work updating eCart 5 to 6, but I'm not so sure with skipping a version.
You might want to sign up for an hour of premier support. I could help you get it updated and avoid any unnecessary work.