Start with unplugging the router overnight. Next, I would rename the router in the settings, and change (or enable) the password to get into the settings, and make it different from the WiFi password. Next, turn off WPS. Set the encryption scheme to WPA2, and AES. Choose a long (10+) digit password that does not use any words, and uses a combination of letters, numbers and special characters.
http://www.bu.edu/infosec/howtos/how-to-choose-a-password/