Create bootable drive with windows 8 /8.1

1. Download the Windows Installation Media Creation Tool from here and run it.
2. Select the Language from the first drop-down menu.
3. Then select the Edition of Windows you want to install. Your choices are: Windows 8.1, Windows 8.1 N, Windows 8.1 Pro, Windows 8.1 Pro N and Windows 8.1 Single Language.
4. In the third drop-down menu next to Architecture choose whether you want a 32-bit or 64-bit version of the OS. If your computer has less than 3GB RAM, then pick 32-bit. If it has more than 3GB RAM, pick 64-bit. If you need to see which version you're running right now, right click on My Computer and select Properties. There, you'll see the information you need under Windows Edition and System type respectively.
5. Click Next.
6. Plug in a USB drive to your computer. Make sure that it has at least 4GB space. If there's any important data on the drive, create a backup as this process will erase the pen drive completely.
7. Now you'll be asked to choose where to save the ISO file. Choose USB flash drive.
8. Click Next.
9. You'll see a list of USB drives connected to your computer. Select your pen drive from the list and click Next.
10. Now the Media Creation Tool will begin downloading the ISO straight to your pen drive. When the download completes, click Finish.