How to update from joomla 3.0 to 3.0.1
From Joomla! Documentation
(note: Joomla 3.0.1 will be released at approximately 9am PDT on October 9th, 2012)
This tutorial will show you how to update from Joomla 3.0.0 to 3.0.1, which is a bit different than normal.
If you use Joomla!'s FTP layer please see Note 3 below.
1. Backup your site[edit]
The update process is generally safe, but it's always a good idea to make a backup before updating. So please go ahead and make a backup of your site now.
2. Install the hotfix patch via Extension Manager.[edit]
1 Go to the Install from URL tab[edit]
2 For the Install URL, copy and paste the following URL:[edit]
http://joomlacode.org/gf/download/frsrelease/17575/76677/joomla_3-0-0_hotpatch.zip
3. Install[edit]
If you have any difficulty installing from URL, download the file to your computer and install using Upload Package File.
4. Update to Joomla 3.0.1 via the Joomla! update component[edit]
After getting the success message, go to Components >> Joomla! Update.
Note #1: If you are not getting the "Note: Hot patch for 3.0.1 update is installed" message, then please repeat Step 2 or ask for some help from a trusted developer.
Note #2: If you're not getting the "Joomla! update was found", click on Purge Cache button.
If you see both of the above, Install the Update.
Note #3: If you use FTP, you might have to FTP the update package, which you can download at:
http://joomlacode.org/gf/project/joomla/frs/?action=FrsReleaseBrowse&frs_package_id=6517