You can use these procedures to change the password for the Administrator account on the computer running Windows Server® 2008, Windows Server 2012.

Membership in Administrators, or equivalent, is the minimum required to perform this procedure.

1. Log on to the computer using the Administrator account.

2. Click Start, click Control Panel, and then double-click User Accounts.

3. In User Accounts, in Make changes to your user account, click Change your password.

4. In Change your password, in Current Password, type your password.

5. In New password, type a new password.

6. In Confirm new password, retype the password.

7. In Type a password hint, type a word or phrase that will remind you of your password or, optionally, leave this field blank.

8. Click Change password.

To change the Administrator password in Windows Server 2012

1. Log into your server via Remote Desktop.
2. Press your Windows key and type Administrative Tools.
3. Double click on Computer Management.
4. Expand Local Users and Groups.
5. Click on Users. 
6. Right click on Administrator. Click on Set Password > Proceed.
7. Type your new password in both fields then press OK.