Older versions did not support single click in-admin updates so you need to do the update manually. You’re actually grandfathered into the new update system. You’re free to manually update at any time. You can access your updates from your purchase history page. To have in-admin updates I have to generate a support license key for your purchases. If I do that those support key must be renewed annually (at a discount), if left to expire you would lose access to both in-admin updates and manual updates. So the better deal for you is to continue to manually update. If you would like in-admin updates, I can generate the support keys. If you would like me to do so, let me know.
Hope that helps!