If you have lost or forgotten your password, click on the 'Forgot Password' link on the login page of the apps or the web portal.
To change your password, log onto the website, go to Settings > Users.
Select your name or the user's name who's password you want to change.
An Edit User's window will pop up:
Input the existing password, and type in a new password. Click Save.
If you need to change a password for one of your users, you need to be the admin, and you need to enter your password in the existing password field. (Not the existing users password you are changing) Create a new password entering it twice.