Every time Apple release a new update to iOS, you will be notified and asked to download and install the new iOS version by iTunes and when you click on update button iTunes automatically download a .ipsw file to your PC / Mac. In case you need to use the IPSW file to restore or create custom firmware, you can find the IPSW files in iTunes specified directory. Now the question is, where is the location of downloaded ipsw files?
How to locate .ipsw file on Mac OS
~/Library/iTunes/iPhone Software Updates
Note: The tilde “~” represents your Home directory.
How to locate .ipsw file on Windows
C:\Users\Your Account Name\AppData\Roaming\Apple Computer\iTunes\iPod Software Updates
or another way is to click Start-> Run and copy and paste the following.
%Userprofile%\Application Data\Apple Computer\iTunes\iPhone Software Updates