I just had the same issue. For me, the installation hung because the first thing the update does is a backup of WSUS
database, which was 8GB, and it would run for 24hrs without finishing.
You can check that the backup is being created by looking in WSUS
folder where a folder called {xxxx...
should be created, which should contain a .bak
file.
To get the upgrade working, I did WSUS
3 db optimization (found on Microsoft's website), then run the update cleanup wizard - this took almost 2 days to finish. In the cleanup wizard I did the first option separately (unused updates and update revisions) and then the rest.
After this I run the update and it took few hours to finish but it actually did. Then I shrunk the database and job done! The WSUS
database is now 4GB.