First the bad news. Changing the tables does not work properly with phpMyAdmin because the extended characters are not interpreted correctly! The data are all imported, but the extended ASCII characters (like Ä, Ö, Ü, ß, ä, ö, ü, ..., and many others) are not displayed correctly.
First you have to export all of the data and bring them into the UTF-8 format, and then you have to make a few changes to the table structures. The export with phpMyAdmin works without problem.
Check the Complete inserts checkbox. Now you have to save the exported data with an appropriate editor in UTF-8 format. (This even works with Windows Notepad, as long as the dump is not too large.)
There are really only two fields that have to be renamed!
In the
jos_core_acl_arotable, thearo_idfield is renamed toid.In the
jos_core_acl_aro_groupstable, thegroup_idfield is renamed toid.
These tables can be imported:
jos_bannerjos_bannerclientjos_bannerfinishjos_categoriesjos_contact_detailsjos_contentjos_content_frontpagejos_content_ratingjos_core_acl_arojos_core_acl_groups_aro_mapjos_core_log_itemsjos_core_log_searchesjos_messagesjos_messages_cfgjos_newsfeedsjos_poll_datajos_poll_datejos_poll_menujos_pollsjos_sectionsjos_usersjos_weblinks
The jos_usertypes table is no longer used in Joomla! 1.5.
Menus and modules can be newly configured either with phpMyAdmin or with the admin interface. And you are done.
Note
If you have some experience with phpMyAdmin and MySQL and/or the SQL language, you will be able to upgrade the core components with no problem.
The migration of third-party components can be more problematic. I am positive that migration scripts will be made available soon.
Last but not least, not a lot has changed with tables other than the character set. The bulk of the component developers' work has been done in the source code, which has to be updated to the new version.
A migration guide is being maintained at joomla.org. Make sure you read it.