1.  My Plex media server is running Win7 Ultimate because I had a legacy TV streaming program that wouldn't run on Windows 10.  I quit using that.  I want to upgrade to Windows 10 but I keep getting the "We can't tell if your PC has enough space to continue installing Windows 10" message.  I have 342 GB free on a 465 GB (500 GB) SSD (no recovery partition).  None of the answers online seem to actually solve this.  I don't really want to do a clean install.

The Plex server does have StabileBit DiskPool on it.  I deactivated the license, uninstalled the program, disconnected 7 of the disks, restarted and it still can't tell if there is enough space to install.

2.  Meanwhile, my two other machines, a Windows 10 Pro laptop and a Windows 10 Pro desktop, cannot access the Windows 7 Ultimate computer to map a network drive, etc.  I get a "Cannot access \\Computer" error. BUT the Win7 machine can access the Win10 machines. Same workgroup.  Sharing and discovery is on, drives are shared, etc.

Obvio if I could upgrade it would solve this.
.

Uninstall any antivirus or endpoint protection you're running and see if that helps.

Unplug the tvs.

Install Ubuntu.

Profit.

No.

ETA: that would absolutely not do what I want to accomplish, so no.

Is that the free space on your C: drive where the win7 is installed?
Is that disk dynamic? Some of the same win11 upgrade errors talk about certain versions not liking an install partition that way.

Yes, the free space is on the C: drive.

I'll check if it's dynamic. I don't think it is it's a basic disk.

1. Clone the OS drive to a larger SSD
2. Replace the OS drive with the clone
3. Open Windows Disk Management and extend the C: partition to use the rest of the disk
4. Upgrade to Windows 10

So 352 GB free of a 500 GB SSD and Win10 needs 20 GB (64 bit) and the solution to the  Windows 10 installer being unable to determine if there is sufficient space* is to buy a 1 TB SSD?

Based on Internet search this installer issue has been not uncommon since Windows 10 came out without any consistent answer.

* Not "there is insufficient space".

Are you attempting to upgrade via the Windows 10 update tool or Windows 10 installation media that you flashed to a USB stick?

Windows 10 media flashed to a USB using the Microsoft tool

And worse.  I uninstalled DrivePool, physically disconnected all the drives except the C: drive, and did a clean start (all non MS services disabled).

Same.

Broke down and installed from the CD I had.  It's working so far.

Except Plex broke (Plex Server disappears and isn't running).  And I can access the that machine from my Win10P laptop now, but not vice versa.  This is why I didn't want to "upgrade".

I seem to recall reading a number of years ago that Microsoft had disabled in-place upgrades from Windows 7 to Windows 10 due to security/support concerns.  So you probably have to fresh-install over the top and then reattach your existing data volumes/drives.

I successfully did it (Windows 7 Ultimate -> Windows 10 Pro).  I had to do it from a CD but that was because the USB install had some issue I couldn't figure out (I did one from USB on my game machine last fall: Windows 7 Ultimate -> Windows 10 Pro).

The upgrade hosed my Plex database and since uninstalling the Plex Media Server doesn't remove the hidden files in c:\user\appfiles (which is a hidden directory anyway) I had to manually uninstall those.

Which was frustrating AF but so is life.