Is this the password to your account, modem or wifi?
If it's to the account, call Customer Care at 855-463-9333. They'll reset the password, and generate a new one for you.
If it's the modem or wifi, double check the password and remember it's case sensitive. If you've already double checked, you can try a manufacturer's reset on the modem. Depress the reset button on the modem for 30 seconds, and allow the modem to reboot. This will set the router's login to the default
If you have the newer, triangle-shaped modem (Viasat Wireless Gateway), the username will be 'admin' and the password will be printed on a sticker on the modem.
If you have the older modem (Surfbeam 2 Plus), the username and password will both be 'admin'
Once you gain access to the router interface using the info above, follow the instructions here to change your wifi name and password.