However, there shouldn't be any reason to convert an IPSW file to another format. The IPSW is an archived file format and can, therefore, be converted easily by using any unzip software.
You could then see the different DMG files within the IPSW file, but you can't apply the software update to your Apple device this way - iTunes still needs to use the IPSW file. Since these files are stored as ZIP archives, you can also open an IPSW file using a file zip/unzip tool, such as the free 7-Zip.
iTunes will then apply the IPSW file to the device. When a compatible device (iPhone, iPad and iPod) connected to a computer is in need of an update, an IPSW file can be downloaded automatically through iTunes after accepting a prompt to update the device.
