The Windows 10 November 2015 update was a full upgrade, and in the process it stored a backup copy of the prior version of Windows 10 on your disk. And that’s a good thing … as it allows you to restore back to the prior version of Windows 10.

But that backup copy is taking up 20GB or more of disk space on your system C: drive.

It doesn’t hurt to leave it there.

But once you have been running with the updated Windows 10 for a few days, and things are running well, you may wish to reclaim that 20gb of disk space. You can do so in three easy steps:

1. Startup (run) Disk Cleanup
2. Select Cleanup system files
3. Select to remove Previous Windows installations

Step 1: Run Disk Cleanup

You can start Disk Cleanup by typing in disk cleanup in the I’m Cortana. Ask me anything. search box at the bottom your Windows 10 desktop. Select to open up the Disk Cleanup desktop app, and select your system C: drive.

Optionally, you can right click on your C: drive from File Explorer, select Properties, and click on the Disk Cleanup button.

Step 2: Select to Cleanup system files

When the Disk Cleanup window display, on the bottom left, click on the Cleanup system files button.

Wait a few seconds while it rescans your disk drive.

Step 3: Select to remove Previous Windows installations

It will refresh the list of files that you can select to delete. Scroll through that list and look for “Previous Windows installations”.

On my computer, this was taking up 23GB of disk space.

Click to select this option, and then click OK.  It will then display a final “are you sure” message box. If you wish to proceed, click Yes.

That’s it!