How you go about clearing the password for an administrator account on a used laptop varies depending on whether you know the current password. If you do, you can clear it and enter a new one via the Users section of the PC Settings screen on a Windows 8 computer. However, if you don't know the password, you must reinstall Windows.
With Current Password
Press "Windows-C" on your keyboard to load the Charms menu, click the "Settings" icon, and then click "Change PC Settings."
Click the "Users" icon to load a list of registered user accounts on the laptop.
Click the administrator account you want to change, and then click "Change Your Password."
Enter the current password for the account in the Current Password field, and then click "Next."
Enter a new password for the account in the New Password field, and then enter this same password again in the Reenter Password field. Enter a password hint in the provided field, click "Next," and then click "Finish."
Without Current Password
Press "Windows-C" on your keyboard to load the Charms menu.
Click "Settings," and then click "Change PC Settings."
Click "General" in the PC Settings section.
Click "Get Started" under the "Remove Everything and Restart Windows" header, and then follow the prompts to reinstall Windows. You may be prompted to insert recovery media or installation discs.