Change file extension on Windows
February 2, 2008 in iPhone How-to & Tutorial
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A filename extension is a suffix to the name of a computer file applied to indicate the encoding convention (file format) of its contents. The filename extensions form are commonly three alphanumeric characters located in the end of the filename after followed by a dot ( . ).
For example: mysong.mp3, myphoto .jpg, mynotes.txt, myspreadsheet.xls, mywordocument.doc, mypresentation.ppt, etc. MP3, JPG, TXT, XLS, DOC, PPT, these are examples of what we called filename extensions. There also many filename extensions which are more than three alphanumeric characters.
In Windows, those filename extensions are not displayed in Windows Explorer by default.
In order to change filename extension, first we need to display the filename extensions.
How-to display filename extension?
Click My Computer → Click Tools in menu bar (or press and hold ALT + T keys) → Folder Options
Click tab View and unselect the Hide extensions for known file types option, then click OK.

Now, every files has its own extension after the dot sign. Right click on the file → Rename then you can change the filename extension to desired one.
For example:
I will rename mysong.m4a to be mysong m4r. So, I’m changing the m4a extension to be m4r.
I will rename myfirmware.zip to be myfirmware.ipsw. So, I’m changing the zip extension to be ipsw.
and so on.

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[...] If you can’t find the iOS 5.0.1 Beta IPSW file in the browse window, ensure that the extension is correct (.ipsw). Change the filename extension into .ipsw. (See: Change file extension on Windows) [...]