You will have to log into the router and disable the setting. Most routers you can access with a web browser from any computer on the network. Exactly how it is done changes from router to router... Do you know what make/model of router it is?
For example, to access a Linksys router if you didn't change the settings, go to the web address:
http://192.168.1.1 and login with no username and password 'admin'