My existing Joomla install is running 1.5.22. I see that the version used by the One-Click install is 1.5.24 and Joomla’s official site says the latest version is 1.5.25. How do I go about updating my current installation?
Looks like Joomla will have internal update process that will allow users to update from the admin panel in joomla. Suspect this will make it unneccessary to have DH do any major work on future updates. Suggest that they put a 1.6 or 1.7 as a first time one click to get users started. Info on 1.5 to 1.6 upgrade sounds painful, but there is a tool that may allow it to be easy depending on how many things are custom in your install. Information is here: http://docs.joomla.org/Migrating_from_Joomla_1.5_to_Joomla_1.6
As joomla 2.5 was released, it seems they actually have a built in update feature . I used Akeeba Admin tools to upgrade my site to 1.74 (as 2.5 was not an option yet) and then plan on upgrading from there. As a side not. #rd party apps will have to be upgraded to. Best course is to disable them before upgrade and plan carefully.
Here is their post on new features.