1. Go to http://192.168.42.1/login.htm and log in to the router.
2. From the Wifi Settings on the right:
a. Choose one of the four networks (2.4GHz, 5GHz or either Guest),
b. Change it's Password on the right (make sure you remember what it is), and
c. Click Save Settings.
First, it's best to do the following while using a LAN cable connected device. If you do it with a WiFi device, you're going to get booted the second you click Save Settings after changing the password for the band that device is currently connected to.
Go to this modem page and use admin as the password. On that page you can change the password for the 2.4GHz band. Make sure to click Save Settings after changing it. If you need to change the 5GHz password, click on the 5GHz header and change the password for that, then click Save Settings. And, of course, make sure to write down your new password(s).
This PDF may also help. Specifically section 6, which is titled "How do I manage my built in WiFi modem?"
Hope this helps. :)
Edit: I should add that there's no video that explains the procedure, or at least not that I know of. It's a good idea, though.
