(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