In order to disable the Guest Access on the Linksys EA7500, first of all, you have to login into the router's web interface by visiting http://192.168.1.1 or http://linksyssmartwifi.com
On the Left-hand side of the dashboard, you need to choose Guest Access
Under Guest Access window there is one ON/OFF button, using the help of that button you will be able to disable the Guest Account.
Once you disable the Guest Access you need to hit OK to apply the settings.
This is how you can disable the Guest Access of the router.