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.