Extract the zipped package downloaded from ThemeForest to your desktop. In the extracted package you will find the knowledge-guru.zip file which is an installable WordPress theme.
You can install the theme in two different ways:
1. WordPress theme uploader
Navigate to Appearance -> Themes to access the theme uploader screen and use the knowledge-guru.zip file.
Extract the knowledge-guru.zip file and upload the extracted knowledge-guru folder to /wp-content/themes/ folder on your server. You will have to use FTP software, like FileZilla.
After uploading the theme, you have to activate it. Navigate to Appearance -> Themes page to activate the theme.