Just close the downloaded. It should save your progress, and then exit.
After that, just rerun the download, and it will pickup where it left off before.
Patching takes ages. You can download the patches individually from here and then patch manually. Instructions on how to do so are also in the link. I found that Blizzards downloader is really slow and completely screws up my internet connection, so this worked really well for me.
I'm on a page about incorrect corrections, and spent the better part of like two hours trying to get someone to understand that -5^2 = -25, not 25, and then that post had comments get reposted because that group is self sustaining, and that person was in turn trying to explain what I just explained to them. And I'm taking that as a victory
I will be AFK for a couple of days you guys hold down the fort while I am gone. I will be checking in on my phone but that will severly limit me. Be back saturday!