Being an Windows Insider, I got my Windows 10 updated very often – let’s say – once a month … and sometime it happens that the updating procedure stops with an error! Looking into the Microsoft Community forum you can see that you are not alone … and possibly you can find there a solution: most of the times it is sufficient to repeat the installation to get it properly work.
However yesterday I got the strange 0x80240031 error during the update to the newest preview release: it is an error related to INVALID_FILE (File is not of the right format). I tried, however without success, several suggestions – like the following – that could be useful in similar situations :

• Reset Windows Update components
• Perform a clean boot in Windows
• Reset Windows updates
• Fix Windows Update errors by using the DISM or System Update Readiness tool
• Troubleshoot problems with installing updates
• Run the Windows Update Troubleshooter
• http://answers.microsoft.com/en-us/windows/forum/windows_10-update/reset-windows-updates/2e26953d-58c4-4704-b627-4a743e87e15c?auth=1
• http://answers.microsoft.com/en-us/windows/forum/windows_10-update/windows-10-update-error-0x80080005/f1d2260f-edc6-4d9a-a1f7-bf400086383d

The simpler solution that fixed my problem was to change an advanced option in the Update section, so forcing a new download of the update setup file. Therefore you can try this easy procedure too:

Go to  Settings -> Update & Security -> Windows update, click on Advanced Options and then on Choose how updates are delivered. Then turn the Update from more than one place switch to OFF and, going back to the Windows Update page, try a new check again.

Settings -> Update & Security -> Windows update – Advanced Options – Choose how updates are delivered