Basically you need to configure the router from one of the hard wired computers already connected to it. Open an internet browser and type in http://192.168.1.254 in the address. This will bring up the routers internal configuration screen. Login with the username admin and the router's serial number for the password.
You didn't say if you wanted wireless or not so these directions are how to disable it. With it disabled there is no other encryption changes necessary. You should now be in "expert mode". Click configure, LAN, wireless (in the other LAN options box). If the enable wireless check box is checked make sure to uncheck it to turn if off. It it is already unchecked leave it alone, wireless is already disabled. Click Submit and you are done.
From what I was reading, the router should ship with wireless turned off but better off checking yourself to be safe. If you need more help or want wireless enabled with encryption post again.
George