I’‘m reading the upgrade guide and it all seems pretty well straightforward. Except for those of us not using the embedded database. I’‘m using mysql 5 and I really can’'t afford to loose anything with the DB, I plan of course of doing a full backup before I do the install.
If you are using an external database then there is nothing you should worry about. The open source version of Openfire does not include changes to the database. The reason why the embedded database is different is that the name of the files used for storing the data has changed.