Follow the steps below to manually update the theme:
First, you download the new theme package from themeforest. You have to log into your themeforest account and navigate to Downloads tab. You find the Gon theme in your purchased themes list.
You can delete the current theme. Don’t worry about this. Your data won’t be lost.
You upload the new theme package via WordPress or FTP software.
Please ensure that you only upload the installable wordpress file. If not, you may get an error message: The package could not be installed. The theme is missing the style.css stylesheet.
You update the theme through the Envato Toolkit plugin. Follow the steps below to set up this plugin:
Download and install the Envato Toolkit plugin
You log into your Themeforest account. Under Settings > API Keys, you generate an API key. Get it.
In WordPress admin panel, you find the section called Envato Toolkit. You input your envato username and API key.
Please read this tutorial Envato Toolkit to get more information.