There is something you must pay heed to. If you extract the Zip file, the result is another compressed file, this time in .7z format. I guess it was a mistake by the programmers. If you've extracted it directly, you'll have the image still compressed. I've already installed the new firmware and it gave no problems.
For those who don't use .7z-unzippers,
here you have the files in a normal ZIP package. I recommend you to get
7Zip or
IZArc though. They're very great programs which understand practically every format, including .7z and they are very functional too.