If automatic update doesn't work for you for some reason, you can always update the theme via FTP. To do this, follow the steps below:
1. Download the theme from ThemeForest.
2. Extract the downloaded .zip file into a folder.
3. Use an FTP client (like FileZilla) to access your host web server.
Note: If you don't know your FTP credentials, contact your hosting provider support so they can provide them.
4. In the file browser, navigate to /wp-content/themes directory.
5. Drag and drop the extracted theme main folder into the directory.
6. The FTP program will give a warning that there is an existing directory with the same name, choose Replace All.
7. Once done, check the theme version in WordPress admin dashboard.
Note: After updating the theme, it is highly recommended to update the bundled plugins. To learn how, check out this article.