Thank you very much for liking our program!
If you have downloaded the LITE version from the Mac App Store, then I'm afraid that there's no way to upgrade it without downloading the unlimited version. The only good thing, it's that when you'll install the paid version, it'll find all the data that you've already saved with the LITE version.
If instead of the LITE version from the Mac App Store, you have downloaded the version from our website, then it's possible to buy a license without redownloading the program. But from your message, I think you have the LITE version from the Mac App Store, so, no luck.