Windows Update keeps what it downloaded, and sometimes forgets to clear it

Windows downloads updates, applies them, and is meant to clean up afterwards. Usually it does. When it does not, the folder involved has a name nobody recognises and a size that can run to several gigabytes.

The three folders

What clears itself

The Download folder empties after updates install successfully. Delivery Optimization has its own cap and clears on a schedule, and both appear in Settings, System, Storage, Temporary files as removable categories. On a working machine none of this needs attention.

When an update is stuck

A download that keeps failing and restarting leaves partial packages behind, and the folder grows. The supported reset is to stop the services, rename the folder, and let Windows rebuild it:

net stop wuauserv
net stop bits
ren C:\Windows\SoftwareDistribution SoftwareDistribution.old
net start wuauserv
net start bits

Renaming rather than deleting is the important part: Windows recreates the folder on the next check, and if something goes wrong the original is still there. Once updates are working again, the .old copy can be deleted.

Delivery Optimization

This is the peer to peer cache that lets your PC get update parts from other machines on your network and share its own. It is capped and it clears itself, and it can be limited or turned off in Settings, Windows Update, Advanced options, Delivery Optimization. Turning it off entirely means every update comes from Microsoft directly, which on a slow connection is a worse trade than the space is worth.

The log files nobody mentions

C:\Windows\Logs\CBS collects servicing logs and, on a machine with a repeatedly failing update, can reach gigabytes on its own. Measured on the same machine, C:\Windows\Logs was 66 MB, which is what normal looks like. If yours is far larger, the size is a symptom of an update failing in a loop rather than something to clear and forget.

The store those updates are servicing is next door, and it looks far bigger than it is.