How do you safely free up disk space on Windows?
When the C: drive turns red, here is the order for reclaiming 10-40 GB using Windows' own tools, without deleting personal files.
Short answer
Open Settings > System > Storage, go to Temporary files, tick Windows Update Cleanup and Delivery Optimization Files, then click Remove files. Next turn Storage Sense on, empty the Recycle Bin, and sort Apps > Installed apps by size to uninstall what you never open. These three moves typically reclaim 10-40 GB and take 20-30 minutes.
What you need
Step by step
Check how much space is left
Press Windows key + E to open File Explorer and click This PC in the left pane. If the bar under drive C: is red, you are below roughly 10 GB. Write down the free-space number now, because that is how you will measure what you gained at the end.
Open the Storage screen
Press Windows key + I for Settings, then follow System > Storage. The screen spends a minute or two calculating the first time you open it. The list at the top shows how many GB each category holds, such as Apps and features, Temporary files and Documents, so you can see the biggest offender immediately.
Clear the temporary files
On the Storage screen click Temporary files. Tick Windows Update Cleanup, Delivery Optimization Files, Thumbnails and Recycle Bin, then press Remove files. Windows Update Cleanup alone can be 3-25 GB. Deletion takes 5-15 minutes, so do not shut the PC down while it runs.
Remove the previous Windows installation
If the same Temporary files list includes Previous Windows installation(s), that is the Windows.old folder left behind by a version upgrade, usually 8-25 GB. Tick it and delete. But if there is any chance you will want to roll back to the older version, wait out the first 10 days; Windows deletes it on its own.
Turn on Storage Sense
On the Storage screen switch Storage Sense to On, then click into it and set "Delete files in my recycle bin if they have been there for over" to 30 days, and the same 30 days for the Downloads folder. Windows will then repeat the cleanup whenever space gets tight, so you are not doing this by hand again in two months.
Uninstall large apps you never use
Go to Settings > Apps > Installed apps and pick Size (large to small) from the Sort by menu at the top right. For the games and programs at the top of the list that you have not opened in months, click the three dots and choose Uninstall. For Steam and Epic titles, removing them from the game launcher's library gives a cleaner result.
Find and move the big files
Install WizTree or TreeSize Free and scan drive C:. Videos, installers and backups over 1 GB show up within minutes. Delete what you do not need and copy what you want to keep onto a USB stick or external drive. Never delete the source file before you have confirmed the copy finished.
Switch OneDrive to Files On-Demand
Click the cloud icon in the taskbar, open Settings and enable the option to save space by keeping files in the cloud (Files On-Demand). Right-click a synced folder and choose Free up space, and the files stay in the cloud without occupying disk. When you are done, re-measure free space from the This PC screen.
Tips
Watch out
Do not try to delete files inside the Windows folder, Program Files, System32 or AppData by hand; the system can stop booting and the only fix is a reinstall. Also, most free "disk cleaner" tools advertised on download sites bundle unwanted software. Windows' own Storage screen and Disk Cleanup tool are enough for this job.
Frequently asked questions
+How much free space should drive C: always have?
Around 10-15% of total capacity, and in practice at least 15-20 GB. Below that, Windows updates fail to install and the system slows down.
+Is it harmful to delete the Windows.old folder?
No, but you lose the ability to roll back to the previous Windows version. If you wait 10 days after an upgrade, Windows removes the folder itself.
+Is the old Disk Cleanup tool still usable?
Yes. Type cleanmgr in Start to open it, and use the Clean up system files button to reach update leftovers. On Windows 11 the Settings > Storage screen does the same job.
+Is it safe to empty the Downloads folder?
For installers and zip archives, yes, since you can download them again. But invoices, bank statements and photos often land there too, so scan the list before deleting.
+I freed up space but the disk is filling again fast. Why?
Usually game updates, automatic cloud backups, or a program's growing log files. Scan with WizTree once a week to see which folder is expanding.
Sources and verification
Last verified: September 15, 2026. tell us. Menu names follow the English-language Windows 10 and Windows 11 interface; labels differ slightly between the two versions.
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