Right-click the file
Select Rename
Change the file extension after the period
Press Enter
Confirm the change if prompted
Enable file name extensions in File Explorer if the extension is not visible
Open File Explorer
Click View
Select Show
Turn on File name extensions
On Mac, select the file
Press Return
Edit the extension
Press Return again
Confirm the change if prompted
Use a command line if needed
Rename the file with the new extension using the appropriate command
Make sure the new extension matches the file format