You can perform system recovery to reset the administrator password.

(System recovery erases all settings including the account information)

Performing system recovery 

  • Power cycle the phone to start the boot process.
  • When the LEDs turn green, start tapping the Microphone Muted button on the phone and continue tapping until the LEDs turn off.
  • Tap the Microphone Muted button once again.
  • When the LEDs turn red, tap the Volume up button once to confirm the system recovery.
  • The LEDs turn off. The phone starts regular boot. the phone displays the following message: Upgrade the phone to complete recovery.
  • After the phone boots up, set the administrator password.
  • Upgrade the phone to complete system recovery.

Hope this helps, for more information read the "Admin & Installation Guide"