Hi,
You just need to login to this site as the user who made the purchase, then click the My Account link at the top of the page and then click Order History. From there a customer can always download the latest version of the products they purchased. Note that the latest version of Form Wizard Pro is 2.6.0.2 and this version requires mojoPortal 2.3.6.7. You can find your mojoPortal version under Administration > System Information, so make sure you have the right version of mojoPortal before upgrading Form Wizard Pro.
Hope that helps,
Joe