Restarting SP2 Download once cancelled

I have been attempting to update my computer for quite a while now with
Service Pack 2. When Automatic Updates wasn't working with my other
computer, I simply went to the Window's Update site, did a search for new
updates, and it displayed Service Pack 2, at which time it simply installed
it for me.

When I tried to update a second computer with SP2, Automatic Updates simply
failed to inform me that it was available for download. So I once again went
to Windows Update site, however they claim that there is no updates available
for my computer. Yet I KNOW that I still only have SP1.

When I looked at my installation history, and APPARENTLY I cancelled the
download of SP2 yesterday (Sept 5th) when I never accepted it.

So can anyone tell me how to restart the dowload??