1) Download Windows 7 USB/DVD Download Tool from this LINK and install it .
DOWNLOAD
*wait 5sec to skip ads
*wait 5sec to skip ads
2) Launch the Windows 7 USB DVD Download Tool. Click on Browse button and double click to choose Windows 8 ISO installation file.
3)Click on Next and then Click USB device , select your USB key drive and click on Begin Copying
Click on Erase USB device and click Yes
5) Wait for the Windows 7 USB/DVD Download Tool to go through the procedure.
And that is all!