You will have to log into your router to reset the password.
If its an Apple product use Airport Utility or if its another make use the Web browser to log into the routers JAVA control and setup panel.
If use have left the log in as default use the code on the router .
The defaults are usually 192.168.0.1, 192.168.1.1 or 192.168.2.1 or 10.1.1.1 depending on make.
Type that number into the address bar of your web browser and then enter the admin password for the router.
Once you get that far look for the password setting and change as required.