The Release Notes for the update to version 4.006 can be found here.
In addition to the feature description of the major changes, and installation advice, it also (naturally) lists the changes from the initial 4.000 release version. The update is urgently recommended due to it fixing a number of important bugs, particularly related to the Windows 10 Anniversary Update and its potential invalidation of time-based licenses but also to Windows versions with Asian language locale settings like Simplified Chinese.