(For the employee/manager)
Your administrator is the one who can change your username, password or email address on file. Keep in mind that your username is not always your email address - this is up to your administrator on how they setup your account.
(For the Account Administrator)
As an administrator you can add/delete other employees, managers, and administrators. You start with visiting Employees --> Add New to add or Employees --> View --> Edit to change. If you need to change your current information the best thing to do is to add a new user with the new information, and then remove the old one by visiting Settings --> Administrators.