If you set up Windows using a Microsoft email address, you can reset the password at the following link: http://www.live.com

If you set up Windows using an offline account, you can use a password reset drive if you created one while you were logged into Windows.

If the previous options don't work or aren't applicable, you will need to reset your PC back to factory default settings, using a new installation of Windows 10. In order to do this, you can use the Windows 10 Media Creation Tool, which you can find at the following link: https://www.microsoft.com/en-us/software-download/windows10