If you know the current password, then just log in with the sub account and change it the same way you would your primary account.
If you don't know the current password:
- Go to: http://webmail.verizon.net/signin/ and click on: Forgot Your Password?
- This brings you to a prompt: "Please tell us what you forgot." Select Password and click the Continue button.
- Next page says "So that we may access your account, enter your Verizon Online User Name and select the Continue button." - Enter the username for the sub and click Continue.
- When prompted, answer the sub's Secret Question and set a new password.
Or you can call Verizon and have them reset it for you/walk you through resetting it. Options on their Contact Us page.