Windows 10 upgrades using external hard drive

zbook, what did my two screen captures tell you about my situation?

The drive that currently has Windows is too small.
This is the Microsoft requirement for an upgrade:

Hard disk space:

16 GB for 32-bit OS 20 GB for 64-bit OS

In the left lower corner search type: winver and post into the thread the Windows version and build.

It is recommended that you use a larger drive as nearly every 6 months there is a major upgrade.

Windows can be setup so that Windows is on one drive and the applications and files including user files are on another drive.
Move your Windows 10 libraries to a separate drive or partition | PCWorld

So if you don't have other attractive options at this time you could save all of the files on another drive and clean install the latest version of windows to the small drive. Then you can consider better long term options so that you have more flexibility.

Clean Install Windows 10 Installation Upgrade Tutorials

My current version is: 1511 OS Build 10586.1106
Earlier in this thread, a professional user advised me that I would be able to do upgrades with an external drive. So I bought a new external drive based upon that recommendation. Are you sure there isn't any way to use this new drive for my upgrades?

The comment on using the external drive for Windows I was not able to find in the thread.
Can you find it?
If so you may be able to ask how they planned to configure it in that fashion.

The Windows operating system can be on one drive and the applications and files can be on another drive.
For an upgrade you will need free space on the partitions. That is where the drive size is having problems.
You could use compression and get marginal improvement.
Compress or Uncompress Windows 10 with Compact OS General Tips Tutorials
You could download and install tree and see the size consumption of the files.
TreeSize Free - Quickly Scan Directory Sizes and Find Space Hogs

After Windows 1511 there were upgrades to 1607 then 1703 and now 1709.
What was done during each of these upgrades and what is happening now?

Longer term strategy would be to get a larger internal drive.
If this is not an option now then consider saving files to an external drive.
Then clean install windows 10 version 1709 on the internal drive and setting up windows so that applications and files go to the external drive.

Updates (keeping the same version of Windows) takes the least amount of extra space.
Upgrades (changing the version of Windows) requires an assessment of the hardware free space and this is not possible with the current amount of free space.
Installation (is being used as a clean install: deleting partitions, formatting, making an unallocated drive and installing windows 10 version 1709) requires you to save your files so that you can clean the drive.

Thank you for explaining, Zbook. I don't want to do an installation for fear of something going wrong, as right now everything is working. My only real complaint is getting messages every day or two to upgrade Windows, which is annoying. If I understand what you are saying, it seems like I will not be able to simply update my current version, but must either upgrade or install a newer version. Is that correct? If so, I will probably just try to disable the software that tells me to upgrade all of the time.