Not enough storage space
C: is full
Read the complete step before making changes. Stop if unsure or if new warnings appear.
Press Windows + I → System → Storage. Wait for Windows to calculate the categories. Click a category to see its contents.
Open “Temporary Files”. Read each category before checking. Don't choose "Downloads" and "Previous Windows installation" carelessly: they can affect personal files or the return to the old version. Only then click on “Remove files”.
Open the trash on the desktop and check the contents. Get back required files by right-clicking → Restore. Only then select “Empty Trash”; Without a backup, these files cannot be easily restored.
Press Windows + E → Downloads. Sort by size or date and open unclear files before deleting. Move important documents to a convenient location. Only delete files that you no longer need.
Under Settings → System → Storage → Temporary Files, “Windows Update Cleanup” may appear. Only select it after a successfully completed update. It removes old update files; Some updates can no longer be uninstalled afterwards. Wait for the process.
Copy large photos or videos to an external drive. Open some files there to check. Only delete the originals after a successful check and another backup. Never move Windows or program folders by hand.