A Joomla upgrade can be performed directly in the Joomla administrative backend. For users with multiple sites, we recommend updating all your sites from Watchful.li — a centralized site manager for Joomla.
Joomla 3.3.5 and 3.2.6 Security Releases now available
Joomla 3.3.5 Security Update has been released.
This is a security release adressing 1 High Priority -  - Core - Remote File Inclusion and - 1 Medium Priority -  - Core - Denial of Service vulnerability as well as resolves 9 tracker issues.
IMPORTANT NOTE: Joomla 3.3.0 and higher requires PHP 5.3.10 for server that have yet to be updated the Joomla 3.2.6 bridge release that includes the patches for the 2 vulnerabilities is also available which can be used with PHP versions 5.3.1 through 5.3.9. It is highly recommended that servers are update to the latest version of PHP 5.3 for best performance, security and compatibility (current release is PHP 5.3.29). Note that older releases will be prompted to update to Joomla 3.2.4 before upgrading to Joomla 3.3.4
This is a security release addressing bugs and not introducing new features.
Full details can be found in the official 3.3.5 release announcement at joomla.org.