If (for some reason) Windows update isn't working, which oddly I've seen a couple times in the last week when I needed to update Windows 7 in advance of a Windows 10 update (the checking for updates progress bar just cycles and cycles for hours) . . .
You can install update via a "convenience" update.
As an example, here's a convenience update for convenience update for Windows 7 and Windows 2008:
Before installing the update, install the April 2015 servicing stack update from here:
Also - you may need to stop the "Windows Update" service so that the convenience update does not try to check for existing updates since the Windows Update service has already shown instability.