installation of windows 8.1on Macbook 2011.

Have a MacBook Pro 2011. I downloaded Windows 8.1 (ISO file on my Desktop). Using Boot Camp downloaded windows drivers to a USB drive. When I click continue to install windows 8.1 the system doesn't find or recognize the software on my desktop. When I click on the ISO file an ejectable drive with the installation files appear on my desktop.

How do I get Boot Camp to recognize the downloaded Win 8.1 software on my desktop? I have OS X El Capitan v10.11.6 on my laptop.

Any suggestions will be greatly appreciated. Thanks!