Hi Lutz,

If you are unable to update your Windows, try the below steps:

1. First clear up your Temporary Files and Internet Cache, reboot and try again. See if this helps resolve the issue.
2. Disable your Firewall and Antivirus software and try again.
3. Many times, an update may fail to install in the first instance, but  succeeds in the 2nd or 3rd try. So try a couple of times.
4. Use the Windows Update Troubleshooter from Microsoft. It resets Windows Updates settings to defaults.
5. Right-click Computer > Manage > Services > Stop the “Cryptographic Service” and rename the “Catroot2” folder situated in C:\Windows\System32\Catroot to something else like say Catroot2X.
   
   Reboot.
   Now run the update or the installers again. This action will re-generate a new Catroot2 folder and the updates or hotfixes, should hopefully install.

If it still doesn't work, try the below step:

Flush the Software Distribution Folder.
Run Command Prompt as administrator. Enter the following commands one by one: 
net stop wuauserv
net stop bits

Now browse to C:\Windows\SoftwareDistribution folder and delete all the files and folders inside.
If the files are in use, restart your device. After rebooting, run the commands above again.

I hope this helps in fixing the updates issue.

Regards,
Lokesh