A lot of you are probably already operating a Joomla! 1.0.x or a Mambo 4.5.x website and now want to migrate it to Joomla! 1.5.
You have a number of basic problems:
You need to back up the entire website.
The general source-code files need to be updated.
Additional components, modules, and mambots/plug-ins have to be updated.
Any changes that you have made to the programs need to be updated.
Your contents have to survive this update procedure without damage.
Contents with special characters have to be converted to UTF-8.
You can see from this list that an update can become quite complicated. The more you have worked with standard components, the easier it is; and the more individualized your website is, the more difficult it becomes. There are no general valid rules for updates at this time. This means that you have to first collect information to be able to establish an individual update plan for your site.