From the command line : 


reg ADD "HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System" /f /v FilterAdministratorToken /t REG_DWORD /d 0 

reg ADD "HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System" /f /v EnableLUA /t REG_DWORD /d 0


This works on Windows 7, 8, 8.1 and 10.

After you disable UAC, you will have to reboot your computer for the changes to take effect.