Before we get started you will need:
Microsoft has a free utility that will automatically make a bootable USB flash drive from a Windows 8 ISO image file. First, download and install the utility. Don’t worry that it says for Windows 7, it works fine for Windows 8 as well.
Download the Microsoft Store Windows 7 USB/DVD Download Tool, Alternate Link.
Once installed, launch the Windows 7 USB DVD Download Tool from the start menu.
Hit Browse, select your ISO file and then click Next.
Plug in your USB flash drive.
On the Choose media type screen select USB device.
Select your USB drive from the list and click Begin Copying.
This process can take several minutes depending on the speed of your USB flash drive.
Read more on the Microsoft Store Tool site