A filename extension is a suffix that determines the file format. To change it, you have to modify a setting in the Folder and Search Options window that makes the extension visible in the file name. After doing that, you can rename the file and change the extension.
- Enable filename extension visibility
Press the Start button, and left-click on Computer in the menu. Then, left-click on the Organize button in the top left section of the window, and select Folder and Search Options in the drop-down menu. Click on the View tab, uncheck the box next to the "Hide extensions for known file types option" and left-click on the OK button.
- Remove the read-only property of the file
Right-click on the file for which you want to modify the extension, and select the Properties option in the drop-down menu. In the Properties window, uncheck the box next to the Read-only option, and left-click on OK.
- Change the filename extension
Navigate to the folder containing the file you wish to modify, right-click on it, and select the Rename option. Alternatively, you can left-click on the file and press F2. Use your mouse pointer to mark the current extension, and type the one you wish to use. Finally, press Enter, and select the Yes option when prompted to confirm the change.