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.) Use the Envato WordPress Toolkit
http://www.commercegurus.com/2014/09/22/keep-captiva-date-envato-toolkit/
2.) Use the Easy Themes and Plugins upgrade plugin
https://wordpress.org/plugins/easy-theme-and-plugin-upgrades/
3.) Manually via ftp
- download the existing version of your theme in /wp-content/themes/
- put it in a safe backup location
- delete the live version of the theme
- re-upload the latest version