File extensions can often be changed by renaming the file. It's usually not necessary to change a file extension in order to use it, and changing extensions can render a file unusable.Continue Reading
In the Windows Control Panel, click the Appearance and Personalization menu, followed by Folder Options. Open the View tab. Under Advanced Settings, uncheck the Hide extensions for known file types check box.
Right click on the file you want to change. Find the Rename option and click it.
In the text field that appears, delete the file name extension and type a new one. If you are prompted to confirm the change, click Yes.