6
Backup your database and installation, and follow the described steps (some modules may become incompatible, no idea what u are using and on what environment).
Make a list of installed stuff:
Un/Modified XOOPS 2.3.3
ISO/UTF-8 language and database tables (this is important) (can't remember if 2.3 supports UTF-8 by default or not, at this time was away from xoops), if tables are different charset then utf8_general_ci, then u should wait with the upgrade (no idea, if current upgrade script support conversion of tables and content inside without problems)
Installed modules:
PHP Version:
MySQL Version:
Apache Version:
OS: (Hope is not Windows/BSD)
May The Source Be With You!