If a password is forgotten, you will need to use the Forgot Password link from the login page. This will send a reset password link to your email.
If you are currently logged in, and trying to change your password from your Profile, you will be asked for your current password.
If you do not remember your current password, then you will need to Sign Out of your account, and use the forgot password link from the login page.
A staff member cannot remember their password, can I reset it for them?
No, they must reset it themselves. On the login page, they can click "Forgot Password" and enter the e-mail associated with the account. This will send an email with a link to reset their password.