As we don’t want to force you to upgrade to DEVONthink To Go 3 we made it a new app in the App Store. If you purchased version 2 you can upgrade to version 3 for a reduced price.
For this to work make sure DEVONthink To Go 2.7.8 or 2.7.9 is installed on your device and opened at least once. Then install version 3 and buy the price-reduced one-time purchase. You can now safely delete the old version at your convenience.