To find what your wireless security key is go to a computer that is currently connected to your wireless network and open the control panel. Select Network and Internet and then next select Homegroup, then select Print and view the Homegroup password. The next page will have the password.
Just under where it says View and Print the Password there is an option to change the password.
You can also go into the routers internal settings and under the Wireless heading select the sub- menu Wireless Security and you will have the option to see and change the word or phrase that you use for the password and you can choose the encryption method. ( WEP,WPA or WPA2)