1809 has arrived, & installed well for me through Windows Update. But try it this way...
(1) Block "Feature update to Windows 10, version 1809" with WUShowHide...
https://support.microsoft.com/en-us/help/3183922/how-to-temporarily-prevent-a-windows-update-from-reinstalling-in-windo
How to temporarily prevent a Windows Update from reinstalling in Windows 10
You've got to catch it trying to come in. But skip this step, if it isn't there.
(2) Make a Windows system image, at "START, Settings, Update & Security, Backup, Go to Backup & Restore (Win 7)", in case things get bad.
Make the Repair Disc to restore it with, or ask Cortana for "Recovery Drive" to make it on USB. Also, see...
https://www.winhelp.us/restore-a-system-image-in-windows-7.html
Restore a System Image Backup in Windows 7, 8, 8.1 and 10
Note: That's a 3rd-party site. The literature looks good. I know nothing of the links or downloads there.
(3) Try the quick fixes here...
https://docs.microsoft.com/en-us/windows/deployment/upgrade/quick-fixes
Quick Fixes
But be aware the ChkDsk "quick fix" can run for many hours. Maybe just do the Windows version in the
*Properties of C:* at the Tools tab. That ran 8/so minutes for me...

(4) If they exist: Use Disk Cleanup (ask Cortana) to delete
$Windows.~BT, $Windows.~WS & Windows.old. Those will be in the categories "Windows update cleanup" & "Previous Windows installation(s)", after clicking "Clean up system files".
A successful upgrade creates them, but normally Windows will delete them after as little as 10 days. The first two accomplish the upgrade. Windows.old is actually the previous OS.
(5) Try this way to upgrade to 1809, from Installation media...
https://www.microsoft.com/en-us/software-download/windows10
Download Windows 10 - Currently, this is v.1809
Make a Win 10 Installation USB drive or burn an .iso to DVD.
As the article says, match it to the Edition (Home, Pro, etc.), Language, & Architecture (64-bit/x64 or 32-bit/x86) of the computer on which it will be installed.
Instructions are at the site how to use those to do an upgrade. Basically, you boot to Windows,
plug in the media, open it in File Explorer, & click
Setup.exe. It will run a bit over an hour. Here are the screens you might see...
https://www.tenforums.com/tutorials/16397-repair-install-windows-10-place-upgrade.html
How to Do a Repair Install of Windows 10 with an In-place Upgrade
Good luck, & keep us informed.