Hi apurrinkitten
That is a setting on your router, rather than a setting in Windows . . .
On the back or bottom of your Router is a sticker with a UserName, Password and IP address (something like 192.168.0.1) printed on it
Note those down
Go to your PC and open a Web Browser
In the address type the IP address and hit Enter
That will bring up your routers configuration page
Somewhere on that page you will find settings
What you need to change is the SSID (the name of your WiFi Network) and the password
Before you can change that, you will need to enter the UserName and Password you noted down from that sticker on the router
That's It!