If you've purchased from the Mac App Store there's no license number. It's done through your ID in the App Store.
There's no upgrade path through the App Store (Apple's policy, not ours) so we usually have a short sale when the new version is released in that store.
We do have an upgrade path from the Mac App Store to our own web store version. See Mac App Store Customers at the bottom of this page for those instructions. Which includes taking a screenshot of your Purchased Apps area and emailing desktop sales.