if your stuck on "could not be verified" I had that problem, I had my auto Time/Date set to Apple USA instead of Apple Europe. Make sure your automatic date and time update is set according to your country. After I set it to Europe I was able to update.
After update, all seems well using my test SSD on my Asus Deluxe 170, did noticed the apple magic mouse is not lagging at all. Just need to wait for my nvidia software update for my gtx 980. After that is done, I'll be updating my main SSD Drive.
My Z77-DS3H build did the update with no issues. But having problems with my HP Probook with the verification issue. My Macbook has updated after 6th attempt. My Sandy bridge hack went thru with no issues also my Quad core Xeon hack also. Just my HP Probook which won't update.