Yes, you can upgrade to a "higher" version of Site Store Professional by simply paying the difference in the license fee.

Many developers and designers purchase the PayPal or Enterprise version and then upgrade later to the Developer version when they resell additional ecommerce sites.

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 - You can upgrade from the PayPal version to either the Enterprise or Developer version.

 - You can upgrade from the Enterprise to the Developer version

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To upgrade your existing Site Store Pro version (license) to a different product version, please submit a trouble ticket and we will send you an invoice link to pay the difference.

After you have upgraded, your myaccount manager will contain both your original version and the new, upgraded version for downloading.

We now offer the option to purchase additional activations as a stand-alone (a la carte) item, see link below for more information:

http://www.sitestorepro.com/store/item_view.asp?estore_itemid=46342279