First of all make backup of your current theme version. In case something goes wrong while updating, you will be able to restore it from a backup.
Login your Themeforest account and download the new theme version from "Downloads" section.
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Extract theme zip package. Find there theme zip archive. Extract it too.
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Upload theme folder via FTP to wp-content/themes replacing old theme files.
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After the theme is updated, go to Options section in your admin dashboard and resave settings.
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After the theme update, you get notification to update all required plugins. For this go to Appearance>Install Plugins section and update plugins there.
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If you don't get notifications to update plugins and you don't have section "Install Plugins" in Appearance section, it means that all your Crumina plugins are up-to-date.