Administrator password lost for late 2013 MacBook Pro with Yosemite
First of all - restart your computer. Press the Command and R keys at the same time when the grey screen appears and hold them until you see the Apple logo. A small loading bar will appear under the logo. Sit tight as your system boots into Recovery Mode.

Click the Utilities tab in the top menu bar, select Terminal, type resetpassword and press Enter. Close out the Terminal window and behind it you will find the Reset Password utility. All you have to do now is select the user account you want to reset, enter a new password or leave it blank and click Save. Then just simply restart the computer from the Apple menu and login with your new password.

However if the user was protected by FileVault or Firmware password, you will probably need to clean-install OSX.