Download the Windows Automated Installation kit from microsoft.com/downloads/. While the file downloads, ensure that the WIM file from which you wish to make an ISO is located in the root c:/ directory. (Name it discovery.wim for ease of use.) When the Windows Automated Installation has downloaded, follow the prompts to install the software.
Open the Deployment Tools Command Prompt Open the Start Menu in Microsoft Windows and click "All Programs" then "Microsoft Windows AIK". The Command Prompt is in this folder.
Open a Windows Preinstallation Environment and copy the WIM file into it; do so by typing "CopyPE C:\Winpe" to create the environment, then "Copy /y c:\discover.wim c:\Winpe\ISO\Sources" to copy the file into the environment.
Navigate back into the PETools folder by typing "Cd C:\Program Files\Windows AIK\Tools\PETools".
Type "Oscdimg -n -bc:\winpe\ISO\boot\etfsboot.com c:\winpe\ISO c:\.iso" to create an ISO image from the contents of the Preinstallation Environment (your WIM file).
* Alternatively, if the WIM image to be converted to ISO is larger than a standard CD (700 MB), type "Oscdimg -m -bc:\winpe\ISO\boot\etfsboot.com c:\winpe\ISO c:\winpe.iso" at Step 4.
Make a disc from your ISO image using a utility that can burn CD or DVD media.