This article assumes that you will be connecting to the router via Ethernet.
To disable the wifi, go into the "Insty Router Settings" at http://192.168.8.1 and put in your admin password.
Then, go to "wireless" on the left hand menu, and then click the green "on" switch for both the 2.4 and the 5ghz to shut them off.
MAKE SURE you're linked up to the router via ethernet before you do this :) - or you'll lose connection to the router and then you'll need to link up via ethernet in order to do anything else.