Open Windows Update by swiping in from the right edge of the screen (or, if you're using a mouse, pointing to the lower-right corner of the screen and moving the mouse pointer up), tapping or clicking Settings, tapping or clicking Change PC settings, and then tapping or clicking Update and recovery.

Tap or click Choose how updates get installed.

Under Important updates, choose the option that you want.

Under Recommended updates, select the Give me recommended updates the same way I receive important updates check box.

Under Microsoft Update, select the Give me updates for other Microsoft products when I update Windows check box, and then tap or click Apply.

http://windows.microsoft.com/en-us/windows/turn-automatic-updating-on-off#turn-automatic-updating-on-off=windows-8