AutoVer plugin will automatically version your CSS and JS files in the generated html page (e.g. style.css?ver=1359464809).
autover.ziparchive into the
Alternatively go into your WordPress dashboard and click on Plugins -> Add Plugin and search for AutoVer. Then click on Install, then on Activate Now.
Install and activate the plugin according with the Installation instructions. The plugin will automatically start to version your CSS and JS files that are correctly enqueued into WordPress (by using wp_enqueue_style and wp_enqueue_script functions).
Depending on the caching mechanism used, a purge of page (html) cache might be needed.
If you want to version only CSS or only JS files, please check the plugin settings by going to 'Tools->AutoVer' from your WordPress dashboard.