To update to the latest version of the theme you have a few options.
NOTE: Before updating the theme we strongly recommend you backup your live theme instance first! We also highly recommend you first conduct updates on a staging/development version of your site to ensure you conduct a full test of major theme and plugin updates in a safe environment before going through the same process on your live site. (Good WordPress hosts like Siteground offer the option of testing theme and plugin updates in a safe staging environment) - http://www.commercegurus.com/siteground
We also assume in this update process that you have made no changes to the theme files yourself. If you have you will first need to move those changes to a child theme. We include a starter child theme in the main zip package which can be downloaded from themeforest. You can read more about child themes here:
http://www.commercegurus.com/2014/09/26/starter-child-theme-captiva-released/
http://codex.wordpress.org/Child_Themes
1. Go to your ThemeForest account and download the latest version of the theme. The Installable file only version.
2. Install this plugin on your site: https://wordpress.org/plugins/easy-theme-and-plugin-upgrades/
3. Upload the new version of the theme via: Appearance > Themes > Add New
4. Go to 'Plugins' and disable CommerceGurus Toolkit, Layerslider and WPBakery
5. Go to Appearance > Install Plugins.
6. Update all 3 plugins and re-enable.
Video on how to update plugins that come within a ThemeForest theme: