Joomla.org has a new release ready for you to download, version 1.5.17.
This release is a fix for release 1.5.16 and it brings you extra security for your website.
Upgrading from 1.5.15 to 1.5.17 is as easy as ever.
Download the upgrade package for your websites current version and unzip all the files in a directory on your hard drive.
BackUp your site before the next step!
Upgrading the standard
Once unzipped go to your FTP program and upload all the files (maintain the directory structure!) and overwrite the files on your server.
Login to you site an check the top right menu in your control panel, just above it it should state 1.5.17.
Upgrading the SEF Patch
If you have implemented the Joomlatwork.com SEF patch before, you have to do it again or you will loose your rankings as you won’t see the titles you have optimized.
Download the SEF patch from http://www.joomlatwork.com At the time of writing the latest patch is called 1.5.176 and it says it the patch for 1.5.16, but if you download it you will see version 1.5.17.
Unzip the package and upload it via FTP that same way as you did with the core update.
Overwrite the files you just uploaded and again maintain the directory structure.
Check if the title pages in you browser title bar are back to what you created before and your are done.