(1) It will seek to come in again. Buy yourself some time 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

I've got it hidden myself. You've got to catch it trying to come in again: "Feature update to Windows 10, version 1803". It will look like this when hidden...

(2) Then, make a system image, at "START, Settings, Update & Security, Backup, Go to Backup & Restore (Win 7)", in case next time it is even worse. Make the Repair Disc to restore it with, or ask Cortana for "Recovery Drive" to make it on USB.

(3) Try the upgrade once more, but download it from...

https://www.microsoft.com/en-us/software-download/windows10

Download Windows 10 - Currently, this is v.1803

Make a USB Windows 10 Installation drive or burn an .iso to DVD. 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 may work better this way. Here are the screens you should see...

https://answers.microsoft.com/en-us/windows/forum/windows_10-windows_install/how-to-upgrade-to-windows-10-version-1803-spring/617a37da-8fc0-4f33-a3eb-59fe9082f925?messageId=a241803d-31c3-4720-b0e4-9002a989ea3c

How to Upgrade to Windows 10 Version 1803 Spring Creators Update Using ISO File from Versions 1709, 1703, 1607, 1511 or 1507

Hi PCR,

Thank you for your help.

I followed your instructions made a system image etc.  But could not create a recovery usb.  It failed saying some system files were missing.

I attempted to run the update again using a usb disk create with the win 10 april 2018 update as you described.  It worked fine until after the first reboot after which it hung at 30%.  I finally after a couple of hours, rebooted and the system restored to the previous version.  After login a Windows 10 setup window opened with the following information: 

"We couldn't install Windows 10.  We've set your PC back... 0xC1900101-0x30004 The installation failed in the FIRST_BOOT phase with an error during INSTALL_RECOVERY_ENVIRONMENT operation" 

It also had a troubleshooting tip link which took me to:  https://support.microsoft.com/en-us/help/10587/windows-10-get-help-with-upgrade-installation-errors 

I plan to work my way down this list before trying again, unless you recommend otherwise?

Regards, 

mike

Update:  Success

What did I do differently:  After the error message noted in my previous reply, I followed all the steps in:  https://support.microsoft.com/en-us/help/10587/windows-10-get-help-with-upgrade-installation-errors  and the ones in which I made specific changes were:

5.  Unplug extra hardware.  Specifically I took all my non-essential USB connections off.  Including - two 2tb usb drives, my usb hub with 1 ssd drive, printer, and fingerprint reader.  This left only the keyboard and mouse connected via usb. I also left the wired ethernet and wireless (built in) connected.

7.  Repair hard-drive errors.  Ran chkdsk /f c:

9.  Restore and Repair system files.  Ran DISM.exe /Online /Clean-image /Restorehealth from an Admin Command Prompt.

Performed a restart.  I had reenabled Windows Update earlier and by now the 1803 update had downloaded and was awaiting install. So I let it proceed instead of using the usb version.  The update proceeded without fault in a normal amount of time, compared to my other machine.

I hope this helps.  mike