There are two ways to change the Administrator password on a Windows server core server, both should be familiar to you.

Method 1:

• From the command prompt on the Windows Server 2008 Core server, type the following command.

  net user administrator *
  

• You will be prompted for a new password and then prompted to re-type the password.
  
  

Method 2:

• Press Crtl+Alt+Del and click on the "Change Password" button.
• You will be prompted to enter your old password (read current password) and then to type and re-type your new password.
• Click on the arrow to complete the change.