Here's a brief lowdown (taken from the Synchronated SWOS web site) of what's contained in the update. The full readme file contained in the archive features a more detailed description of what's new.
"Full leagues, all divisions from 68 countries - the entire SWOS database [has been] updated.For more information, and to download the update files please visit the Synchronated Sensible World of Soccer Updates site at http://synchronated.110mb.com/
All national teams [have been] updated. [The] 'classics' league [has been] updated with newly retired stars.
Fully playable and tested career mode functionality with league structures modified to fit current real-life divisions.
new 'expanded' update included which adds extra clubs in order to expand the few partial leagues to full size"