How to Change File Extension in Windows 7

Change and view file extensions of all file types in windows 7 using folder options. No need to install any new programs.
  1. Open Windows Explorer or Computer
  2. After the window opens, click on the Organize button present on the top-left corner of the window just below the Back & Forward buttons as shown in the picture
  3. A dropdown menu opens displaying a list of options. Click on Folder and search options
  4. After Folder Options window opens, go to the View tab
  5. Unmark the checkbox Hide extensions for known file types and click OK
Now select the file for which you want to change the extension and Rename it. This allows you to change the extension of file as well along with its name.