Previously, I posted an article on how to install Windows 10 build 10240 on the listed devices (930, 640, and 640xl). But as time passed, the download links to these firmware packages expired making it pretty difficult to download and flash this firmware on our Lumia.
Today, I took some time to search for these firmware files so you can flash and enjoy Windows 10 on your devices. Thanks to mspoweruser.com for the download links.
To download this firmware and view its flashing guide please follow this link to the original post.