NR5307 Supervisor Password

I can use admin account to access SSH and Telnet, but I found that this router has a higher privilege account (Supervisor and root). Why can't I get the password to access it? What is the purpose of ZYXEL to keeping this account? Thank you! My SN is S240Y47026135 and Firmware Version is V1.00(ACJT.0)C0.