How to update Boot Camp 5

I installed Windows 8 last month with the previous version of Boot Camp.

Now that Bootcamp 5 is out, I want to update Boot Camp but I do not understand how. I've downloaded the files from Apple's website, put them on a FAT formated USB drive, and clicked the setup.exe file within the Bootcamp folder. I get the follwing message: "This app can't run on your PC. To find a different version for your PC, check with the software publisher."

Is there a way to update Boot Camp for my Windows 8? Or must I reinstall Windows 8 with Boot Camp already updated? Can I simply download the Bootcamp files to my desktop and open them from there? What's the need for the USB?

Any help is appreciated.

Thanks.

MBP late 2010, Mac OS Mountain Lion, Windows 8 Pro