You have to run the setup file on a Windows machine. If you want 64 bit Windows then you must run the setup on a 64 bit Windows machine.
Once the download is finished (about 3GB if I remember correctly) you will get the option to create install media.
Select that then check the box for creating an iso file.
Move that iso file to your Mac then start Bootcamp Assistant and point it to that iso file. You'll also need to download the support software again if you've deleted it.
You'll need a 8GB USB stick to put everything on.