[HOW TO] Change Windows Update settings
Surface RT and Surface 2 (and Surface 3, one assumes): Windows Update settings are always on and can’t be disabled. You can’t change Windows Update settings for Windows RT.
Surface Pro and Surface Pro 2 (and Surface Pro 3, one assumes): To change your Windows Update settings:
Step 1: Swipe in from the right edge of the screen, and tap or click Settings, and then tap or click Change PC settings.
Step 2: Tap or click Update and recovery, and then tap or click Windows Update.
Step 3: Tap or click Choose how updates get installed, select the settings you want, and then tap or click Apply. [1]
If, for example, you turned off (disable) automatic updating during set up and you want to turn this feature back on (enable) again, choose
Install updates automatically (recommended).
Source and more: http://www.microsoft.com/surface/en-us/support/performance-and-maintenance/install-software-updates-for-surface
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[1] IMPORTANT! => Windows Defender will only auto-update itself when the Install updates automatically option is selected.