Unable to upgrade macOS Sierra 10.12.6 to 10.13.0.

You don't really tell us what this problem is exactly. :-(

Upgrading a macOS depends upon the model Mac, specifications, and year. To get more information about your computer, choose:  (Apple menu) > 'About This Mac' in the upper left corner of any window, then "More Info..." or "System Report". There's more about this in "About System Information [Profiler] on your Mac" - System Information User Guide for Mac - Apple Support

Use the computer information, including the model year, and the links below to determine what is possible with your computer.

Click on this link to read how to get different versions of macOS --> How to download and install macOS - Apple Support

- The article also has links to system requirements for each OS version which you should check against your exact computer model. For any model produced in the last 5 years or so you should use the system requirements links for each OS version instead. This web site also has a reliable presentation of model and OS version compatibility: https://eshop.macsales.com/guides/Mac_OS_X_Compatibility

- It helps to have more RAM (memory) than what is noted as "minimum" for any particular system or your computer may run slowly.

- You may find you must use Safari to get links for High Sierra and later using the Mac App Store application to open to a functioning page.

- Sierra, El Capitan, and Yosemite download as a .pkg. Click on this to have a converted version placed in your Applications folder as an "Install OS..." application. Run the installer and follow the directions.

- Upgrades may take some time (up to an hour or more) to install, with restarts and blank screens.

- If you encounter download problems it may help to download while in Safe Mode Use safe mode on your Mac - Apple Support

Before upgrading, back up at least your data in case something goes wrong. See this support document: How to back up your Mac - How to back up your Mac - Official Apple Support

Check if your old apps will still work with with the OS you want to install - https://roaringapps.com/apps This is particularly critical if you are upgrading to Catalina or newer, as older 32 bit apps will no longer work. To check for those, try this 32 bit application scanner application --> https://www.stclairsoft.com/Go64/

If an error occurred while updating or installing macOS --> If an error occurred while updating or installing macOS - Apple Support

Definitions:

Update - to apply fixes, corrections and improvements to the current named macOS. A point update.

Upgrade - to appy a major, renamed revision of the macOS onto the startup drive.

If you got your installer from this Apple website (Apple - Support - Downloads), then you don't have the correct installer. Yes, that "macOS High Sierra 10.13.6 Combo Update" DOES require 10.13.x to use it, and when applied properly it does update macOS 10.13.x High Sierra to the final High Sierra version 10.13.6.

To recap:

• You want to upgrade from 10.12.6 Sierra to 10.13.6 High Sierra (because 10.13.6 is the newest, best High Sierra version).

• Apple does not distribute a High Sierra v10.13.0 installer at all.

• Version 10.13.6 is the only High Sierra upgrade installer that Apple distributes today.

• You need the correct upgrade installer to move from 10.12 Sierra to High Sierra 10.13.6 - again, the newest, best High Sierra version.

The only Apple macOS upgrade installer that you can use to upgrade 10.12.6 Sierra to High Sierra 10.13.6 is this:

➡️ macOS 10.13 High Sierra Installer.

Once downloaded, double-click the “Install macOS High Sierra” app now found in your Applications folder to begin the upgrade from Sierra.

Please see > How to download macOS - Apple Support.

Apple does not provide a 10.13.0 Installer, only the full 10.13.6 Installer.

Use the App Store

To download macOS from the App Store, use a Mac that is compatible with that macOS. If your Mac isn't compatible, the App Store dims the Get button, says that the macOS is not compatible with this device, or says that the requested version of macOS is not available.

If these links don't work as expected, try again using Safari, which is in your Applications folder.

Sonoma 14

Ventura 13

Monterey 12

Big Sur 11

Catalina 10.15

Mojave 10.14

High Sierra 10.13

Use these links to find macOS in the App Store.

Cick the Get button in the App Store to begin downloading. Software Update might open and ask you to download from there.

After downloading to your Applications folder, the installer opens automatically. Follow the onscreen installation instructions. Or quit without installing to leave the installer in your Applications folder for later use.

No, you have a combo Update, not the full Upgrade.

Natural confusion exists because of the similar terms,& the opposite meanings in English & Computer lingo...

Upgrade your car & you're likely adding accessories to an already car, Update your car likely means trading it in for a newer model

But here in Computerland.. Update is moving from say 10.12.2 to 10.12.6, 10.13.0 to 10.13.4, or 10.15 to 10.15.6.

WhereasUpgrade is moving from 10.12.x to 10.13.x or 10.4.x, or 10.15.6 to 11.0

For full installers Apple only offers the latest of each version, like 10.2.6, 10.3.6, 10.4.6, 10.5.7 & so on, you got an Updater which requires an earlier version of the same version.