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The safest way to reclaim space after Windows 10 version 1803 is to remove the Previous Windows Installation(s) entry—also known as the Windows.old folder—using Windows’ built-in Storage settings or Disk Cleanup. Do this only after confirming that the upgraded system and your files work correctly: deleting the previous installation removes your ability to roll back. The amount recovered varies by computer; more than 30 GB is possible, but Microsoft does not guarantee or establish it as a typical result.
What the cleanup removes
A feature update keeps a copy of the earlier Windows installation so you can return to it if the new version has problems. Windows presents that copy as Previous Windows Installation(s) in cleanup tools and stores it in the Windows.old folder. It is not an ordinary cache, so do not delete the folder manually while it is in use; use one of the supported cleanup paths instead.
Decide whether it is safe to delete
Keep the previous installation if you are still testing version 1803, troubleshooting drivers or applications, or may need to restore the prior Windows version. Check that Windows starts normally, your applications launch, hardware works, and important files are present before proceeding.
Microsoft says the previous version is automatically deleted 10 days after an upgrade. You can remove it sooner once you are confident, but Microsoft warns: “If you delete your previous version of Windows, this can’t be undone (you won’t be able to go back to your previous version of Windows).”
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Method 1: Storage settings and Temporary files
- Open Start > Settings > System > Storage > Temporary files.
- Allow Windows to calculate the removable files.
- Select Previous Windows Installation(s), or the equivalent previous-version entry shown on your installation.
- Choose Remove files and confirm.
- Open File Explorer, select This PC, and check the available space on the Windows drive.
Interface wording can differ between historical version 1803 builds and later Windows 10 releases. If the previous-installation entry is not listed, use Disk Cleanup.
Method 2: Disk Cleanup
- Search Windows for Disk Cleanup and open it.
- Select the Windows system drive, normally
C:, and choose OK. - Click Clean up system files, then select the system drive again if prompted.
- Review the categories and select Previous Windows installation(s) if it appears.
- Choose OK, then Delete Files to confirm.
- Check free space in File Explorer under This PC.
Review the list rather than selecting every category automatically. Disk Cleanup may show other removable items, but this procedure is specifically for the prior Windows installation.
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Another documented Windows 10 route
Some Windows 10 releases expose the cleanup through Settings > System > Storage > Change how we free up space automatically. Under Free up space now, select Delete previous version of Windows, then choose Clean now. Microsoft documents these labels for Windows 10 versions 20H2, 21H1 and 21H2, so a version 1803 computer may use different wording or may not display this exact path.
How much space will you recover?
There is no official fixed amount for a particular PC. The size depends on the previous Windows build, installed language and optional components, update path, and the files retained on that device. Microsoft’s published update-space figures describe space needed to install updates—not space returned by deleting the previous installation—so they cannot be used as a recovery estimate.
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- Designed to work with Windows or Mac computers, this external hard drive makes backup a snap just drag and drop. Reformatting may be required for Mac
- To get set up, connect the portable hard drive to a computer for automatic recognition no software required
- This USB drive provides plug and play simplicity with the included 18 inch USB 3.0 cable
- The available storage capacity may vary.
A contemporaneous secondary headline promoted “over 30 GB,” but that figure is not a Microsoft guarantee. Use the size shown beside the previous-installation entry in your own Temporary files or Disk Cleanup window as the estimate for your computer.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.If the drive is still full
Removing the previous installation only addresses the rollback copy. If more space is required, first review Windows’ other temporary-file categories and your largest personal files. Microsoft also documents moving personal files to external storage. That is separate from Windows.old cleanup: an external drive does not remove system files, and copying files does not create additional rollback space.
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- Designed to work with Windows or Mac computers, this external hard drive makes backup a snap just drag and drop
- To get set up, connect the portable hard drive to a computer for automatic recognition no software required
- This USB drive provides plug and play simplicity with the included 18 inch USB 3.0 cable
- The available storage capacity may vary.
Quick decision checklist
- Keep it: the upgrade is unstable, hardware or applications are failing, or you may need to return to the earlier Windows version.
- Remove it: the current installation is working, your files have been checked, and you accept that rollback will no longer be available.
- Verify: record the displayed removable size before cleanup and check free space afterward in This PC.
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