Windows 10: Reset Password

Boot Window Installation Media (CD or USB).

Once the setup is loaded and asks for language, keyboard, etc. hit Shift+F10 to open a command prompt.
Issue the following commands:
move d:\Windows\System32\utilman.exe d:\Windows\System32\utilman.exe.bak
copy d:\Windows\System32\cmd.exe d:\Windows\System32\utilman.exe
And reboot using: wpeutil reboot

Once the machine boots up, hit the utility manager icon in the lower left. This will open a command prompt now. Use it to create a new user with administrative permissions like this:
net user <username> /add
net localgroup administrators <username> /add

Once this is done, you should see your newly created user and will be able to log in without a password.

To reset the password of another Administrator use: lusrmgr.cpl