Try running it in safe mode if it is in your download box. Mabe run disk clean up first then click on clean up system file when it opens and check for old Windows updates to see if any there waiting to be deleted and delete them.
You could try running the update in safe mode if it is in your download folder.
Now if you are updating using a wireless connection maybe do it with an ethernet connection as it should finish a lot quicker.
If that fails go to the Windows Update web site and download it from there.