Updating a Theme
It seems scary but you really won’t loose any of your data. The only exception is if you have made edits to theme files like header.php, footer.php etc. These changes will need to made again to the new files. But all of your content and theme settings are preserved.
From your WordPress dashboard, navigate to Themes. Activate a different theme. Then click on Theme Details for your theme. In the lower right hand corner, click Delete.
Once you’ve deleted the old version of your theme, download the new version from your My Account page and install it.
Alternatively, you may want to use a plugin to automate backing up your current theme and uploading the new version: http://wordpress.org/extend/plugins/easy-theme-and-plugin-upgrades/
Where do I download the update?
You can find the latest zip file for your purchased themes under My Account in the main menu. If your past purchases are not listed, let us know.