This is easy. A user can reset the password for their own account by clicking on the Forgot password link at the bottom of the login page.

However, the Account Owner and Account Admins of a multi-user Company Plan can also reset the password of their account's Writer Users via Account Admin > Manage Users.

Simply click on the edit icon to the right of the user's name and you'll be directed to the Edit Writer User page for that user. Click Send password reset email and an email inviting them to reset the password for that account will be automatically sent to the registered email address for that user as displayed in email field.