Flexx is currently at version 4.0.34. You can sign into your membership page (http://ithemes.com/member/member.php) and download the latest version of the theme, or if the sucscription has expired, you can purchase a new subscription from that same page (scroll down to the "Purchase & Renew Products & Subscriptions" section). If you do not have access to the membership page, you can purchase the theme through the Flexx sales page: http://ithemes.com/purchase/flexx-theme-wordpress-blog-themes/
Flexx has seen quite a few updates since version 2.6, but there is no reason to assume that it is not compatible with WordPress 3.3.2. To make sure, you may want to test this on a test domain or locally, before updating WordPress.
hope that helps,