If you want to update your unmodded phpBB2 Forum, you need simply to overwrite all existing Files except your Template folder and config.php. There are no changes to the Database on SEO phpBB, so it’s not necessarily to update the database.

If you have already modded your forum, you have to change the files per hand. The Codechanges that you need to do you can find on http://www.seo-phpbb.org/keyword-in-url.html (german).