Are we talking the modem's User Interface password? If so,
Simply go to 192.168.1.1, user the default username and password.
Click on Advanced tab then go to System Tools under the same tab click on Administration.
It will show you option to change the Default User-Interface Log-in.
See the reference below:
For Wireless or Wi-Fi, on the menu on the left side of the page, click Wireless.
You can change your Wi-Fi details or keep the default settings. The default Wi-Fi SSID (network name) is WiFi-xxxx (xxxx is a random 4 digit alphanumeric code printed on the sticker underneath your modem). By default, the Wi-Fi password is printed on a sticker underneath your modem (Wireless Password/Key). Click Save.
Let us know how it will go.