Just to make sure what you are saying.
I can click on the exiting message that says "Upgrade for your AbanteCart to new version 1.3.3 is now available. Please click --> this link to start the upgrade."
And when it takes me to the Package Installer page and the prefilled text says "abantecart_upgrade_133", I can change that text to read abantecart_upgrade_134, and then click Continue.
So to say it for everyone, as long as you have an original link to upgrade, you can type it the upgrade number. And as you stated previously, upgrades must be done in order, no skipping a version.
If this is all correct, please let me know so I can do it and my customer can start receiving emails when sales are made. THANK YOU Mr. Basara.