First of all, please make sure to download newest theme version from ThemeForest Download section.
Then, just replace the old theme files with new ones on your server via FTP (provided you haven’t made any changes in the source code. If you did, please reapply them to the new version of the theme or they will be lost).
Keep your eyes on potential required plugin update messages at wp-admin dashboard once you replace the files. You should update all required plugins if the updated theme suggests so.
All settings in Customize panel and your content will be preserved.
Note: Once new theme version is online, user who purchased the theme, should get email note from the Envato (ThemeForest).
For more info and detailed instructions please refer to our Online Theme Documentation.