For those who already have 10.13 installed and just need the final update, you can download the macOS High Sierra 10.13.6 Combo Update directly as a DMG file. 2. Preparing a Bootable USB (Optional but Recommended)
If your DMG is already a bootable image (rare), you can use dd : macos high sierra 10136 dmg install
in System Preferences or the App Store to download the latest Security Updates , which will bring your system to version 10.13.6. Terminal command to create a bootable USB for High Sierra? For those who already have 10