Quick answer: Free several gigabytes on C, restart Windows, then retry the update. Start with temp files, Recycle Bin, large downloads, and update cleanup.
Why this happens
Windows Update needs temporary working space in addition to the final installed update. Very low free space can cause repeated failures.
Safe steps
- Pause the update if it is stuck.
- Free space from Temporary files and Recycle Bin.
- Move large personal files off C.
- Restart Windows.
- Run Windows Update again.
What to avoid
Do not delete WinSxS, DriverStore, or installer folders to force an update.
Use DiskTidy for review-first cleanup
Download DiskTidy to scan common cleanup locations and large files locally before deciding what to remove.