The upgrade has been designed to be as seamless as possible and will work with all of your existing "Add to Cart" buttons. The majority of your settings (company information, shipping methods, payment options) will carry over automatically. You will have to make some changes to the cart appearance/theme settings, as these options have changed in our new version.
All of the standard AmeriCart features will be available, but merchant-specific customizations may not carry over (unless these customizations later became standard features).
If you have any specific questions or concerns, please send us a support ticket.