How to change file name extension on Windows
It's not a good idea to change the file name extension because this will result in the failure to find right program to open the file. Either Windows and Mac will prompt you to confirm the file extension change. If you decide to change the file name extension, see how below.
1. Make sure the file name extension has not been hidden.
To avoid change the fine name extension by mistake and cause unnecessary problems, the file extension is hidden by default on Windows. You could change this in Windows Explorer: click on Tools > Folder Options > View, and remove the check of Hide extensions for known file types. Now you could see the full file name such as 'file.wmv'. The file extension is the letters after the dot characters.
2. Rename the file name extension.
First select the file you want to rename the extension, and click twice (slower than double click), or press F2 on keyboard to highlight the text, then replace the file extension to what you want. Hit Enter to confirm.
A warning message shown as above asks for your confirmation. Click 'Yes' and you can open it with its default program.