According to Apple's rules it's not possible to cross-grade to a free world version or upgrade to a higher edition outside of the App Store. Sorry.
Where do I find DEVONthink?
With DEVONthink 3 we have retired DEVONthink Personal. We are now working on making the new generation of DEVONthink compatible to the sandboxing requirements of the App Store. We will let you know via our blog when it has passed Apple's review.
Where do I find my license code?
Apps purchased in the App Store are identified online through your Apple ID. Neither are you sent a license code nor do we receive any information about your purchase.
Why is an app not available in my country?
For varying reasons we do not offer our software in certain countries. If you are living in a country where our software is not available in the App Store you might be able to buy it with e.g. a European or US American credit card.