Joomla! 1.5.18 and Joomla! 1.6 Beta 3 released
For Joomla! 1.5: you can use Akeeba Backup to create a backup, then Sam’s Update Manager to update the Joomla! 1.5 websites you manage to 1.5.18. You can also read the tutorial on how to update a Joomla! 1.5 website, have a look at it here.
For Joomla! 1.6: this beta version is not for use on production websites! It is intended to be used for evaluation purposes only. You can install it to get to know the next great version of Joomla! and report any bugs you find to the Joomla! Bug Squad.