Trying to upgrade to version 1803, and always fails in Windows Update

I'm looking for suggestions for how to proceed. I have an older Toshiba laptop that has been working pretty well with Win 10 ver. 1709 on it for quite a while. I think for as long ago as since last summer, it has been trying to upgrade to version 1803, and always fails in Windows Update. I decided to try using a DVD I have with 1803 on it, and do an In-Place Upgrade, thinking this would overcome the problem. It goes pretty far into the upgrade (over 1/2 hour, at least 37%), and then fails with a simple message that the installation has failed.

I tried it again after doing a disk cleanup of system (old install) files, but it still fails. Admittedly, I am using an older CD I had with 1803 on it. I would like to keep my files and setup. What should I try next? Should I download a fresh ISO of 1803, or one of 1709 (followed by a more recent version), or 1809--which of these will have a better chance of getting a good in place upgrade? Or should I use the built-in download to do a "system refresh"? Otherwise, I am kind of stuck, and it seems like I would have no option but to do a completely fresh install--and then to which version?? I'd rather not have to reinstall all my files and programs, but obviously would have to with a fresh install.

Also, I have most of my files segregated on a separate D: partition. Can i just leave that there if I do a fresh install?

Skip old 1803 and go straight to the latest version goto Download Windows 10 hit update now. 1803 is old and the new version may work

1) Place the computer in clean boot
Perform a Clean Boot in Windows 10 to Troubleshoot Software Conflicts | Tutorials

2) Temporarily detach all hardware (docking station, external drives, USB wireless,etc.)

3) Uninstall non-Microsoft Antivirus, firewall, and drive encryption software

4) Perform an upgrade with the desired windows build using a bootable iso

5) If the upgrade fails then run setupdiag > post a share link into the thread using one drive, drop box, or google drive
SetupDiag | Microsoft Docs

6) Post error codes / messages into the thread

Thanks for the suggestions. I'll try zbook's idea first. Samuria, if I "hit update now" will I be downloading the ISO, or would this lead to an automated on-line update?

I am also trying to understand what happened to this thread. I thought I was replying to a longstanding thread on doing an In-Place Upgrade, and somehow I ended up with a new thread.

When upgrading Windows it can be done with the upgrade assistant or with an iso.
The iso can be downloaded to the desktop or to a flash drive.
For the flash drive the iso can be bootable or non-bootable.

The best option is to make a bootable iso on an 8 GB flash drive.

The bootable iso can then be used on multiple computers (Windows RE, and upgrades).

And if there is a failure to upgrade there often is a more elaborate error code using the iso rather than the upgrade assistant.

For example the upgrade assistant often produces just a result code.
The iso typically produces a result code with an extend code.
The detailed error is more useful in the troubleshooting.

To perform the upgrade with the iso:

a) power on the computer
b) insert the windows 10 iso into any USB port
c) open file explorer
d) identify the iso
e) click on the iso and launch setup or setup.exe
f) follow the text and images in this link:
Download Windows 10 ISO File | Tutorials

I've downloaded the Win10 ISO for ver1809 onto my D: partition. Can I simply run the iso with Windows Explorer to do an In-Place Upgrade? Or should I make a USB or DVD from it?

It will run from the drive allow about 2 hours depending on the pc turn any anto virus off as that can effect it and ensure about 30gig free on c

The in place upgrade can be performed with the iso on the desktop or in documents or on a flash drive.
The setup or setup.exe needs to be launched from the file found within file explorer.

Sorry for the delay getting back to this, I've had a lot of other stuff going on.

As zbook suggested, I put the computer into clean boot. For good measure, I ran Disk Cleanup on system files again, and also deleted manually all the files under Windows\SoftwareDistribution\Downloads. The fact that they did not delete with Disk Cleanup indicates to me there is something else wrong with the Windows installation. The install (ver 1809) went to 37% as before, got stuck there for a while, and then failed with the simple message, "Windows install has failed." And by the way,...the failed installation completely deleted my Downloads folder. (Fortunately, I have a backup.)

Also, when I looked at settings/WindowsUpdate, even after clearing the datastore downloads, and both before and after the install failed, there is a message there that says:

Update Status
Updates are available
• Feature update to Windows 10, version 1809 amd64 2019-04
Status: Awaiting install
Updates are ready to install

The latest feature update to Windows is ready to install! It's been waiting for you to kick it off. These improvements help Windows run smoothly and securely. Select this option to kick it off:

Yes, this is in red. Of course, I've already tried this install several times, always fails. Given the nature of these failures, I suspect I am not really going have much option but do a fresh install of Windows. I have not run setupdiag, and I am not feeling like it is going to be worth the trouble to try another step.

What do you think?

There is a log collector used in another forum.
Run the BETA log collector and upload into this thread:
BSOD - Posting Instructions - Windows 10 Forums