How can I kick users from my uverse wifi?

My (now ex) friend is being a douchebag and he's using my wifi connection and I need to remove all of his devices from my network, my wife's dad said changing the password will work, is this accurate?|||Yes just change the password.|||yes, as long as no one gives him the password.|||yep change the wep key and if you can get to the routers internal settings ban the mac id's also|||Yes