If you have modified any of the theme files, these changes will be overwritten when updating, make sure you have a backup copy of the changes and make the change again to the new version of the file after the update.
1. Download the latest version of the theme from the Downloads page on ThemeForest and extract the zip file.
2. If you’ve modified any of the theme files, connect to your server via FTP and backup those files.
3. Log in to the WordPress admin and go to Appearance → Themes on the WordPress menu and Activate another theme, such as TwentyTwelve.
4. Click Delete next to the Storm theme.
5. Click the Install Themes tab at the top and click Upload
6. Choose the storm.zip file in the package downloaded in Step 1 and upload the theme.
7. Once the theme has uploaded, click Activate.
8. Go to Appearance → Theme Options and click Save to regenerate the cache.
9. (Optional) If you’ve modified any files, make the modifications again to the updated files.