In plain words
A full disk is like a cupboard with no room left: everything slows down, and Windows can no longer find the space to unpack its updates. You start by looking at what is cluttering it, you throw away the packaging (temporary files), you move to the cellar what you keep but do not use (external drive, cloud), and you never touch the load-bearing walls (the Windows folder).
A nearly full disk slows Windows down and can block updates. To be safe, keep at least 15 to 20% free space. Here is how to get it back, from the simplest actions to the more advanced ones.
1. See what takes up space
Open Settings → System → Storage. Windows shows the breakdown by category: apps, temporary files, documents, pictures, and so on. Click Show more categories for the details.
Tip
To find the large folders precisely, the free program WinDirStat draws a map of the disk where each rectangle is a file, proportional to its size. The biggest ones stand out immediately.
2. Follow the cleanup recommendations
In Storage, open Cleanup recommendations. Windows suggests:
- temporary files and the Recycle Bin;
- large or unused files;
- files already synced to the cloud (OneDrive);
- unused apps.
Tick what can go, then click Clean up.
3. Delete temporary files
Storage → Temporary files. You can safely tick:
- Temporary files, Temporary Internet Files, Thumbnails;
- Windows Update Cleanup;
- Previous Windows installation(s), often several GB after a major update. Once deleted, you can no longer go back to the previous version.
Warning
Only tick Downloads after checking what is in that folder: it often holds files you have not filed anywhere else.
4. Automate with Storage Sense
Storage → Storage Sense. Turn it on: Windows will automatically empty temporary files and the Recycle Bin, and can free up OneDrive files you have not opened for a long time (they stay in the cloud and download again when you open them).
5. Uninstall software you do not need
Settings → Apps → Installed apps. Sort by size, then uninstall what you no longer use with the … button → Uninstall. Games and creative software are often the heaviest.
6. Move rather than delete
- Photos and videos: move archives to an external drive or a NAS. Always keep a second copy.
- OneDrive: right-click a synced folder → Free up space. Files stay visible but are only downloaded when opened.
Going further
These actions need a terminal run as administrator (Windows + X → Terminal (Admin)).
Clean up old versions of Windows components (Windows already does it by itself after 30 days; the command does it right away):
Dism.exe /Online /Cleanup-Image /StartComponentCleanup
Turning off hibernation on a desktop PC deletes the hiberfil.sys file, which takes up about 40% of RAM by default. It also turns off Fast Startup and hybrid sleep:
powercfg /hibernate off
Danger
Never delete the contents of C:\Windows by hand, especially the WinSxS folder, and beware of "registry cleaners": the gain is nil and the risk of breaking Windows is very real.