In order to update the plugins included in the theme you need to :
Install the latest version of the theme.
Go to Plugins > deactivate and delete the premium plugins
Go to Appearance > Install Plugins and re-install the plugins.
If you don't want to update the theme but want to update the plugins then download the newest version of the theme from themeforest, open the theme folder includes > plugins and then upload the zip file of the plugins you want to use to your WordPress.
If you still need help with updating the plugins please create a ticket under Thefox category.