How to change extension of any file in windows 10, 8, 7 or XP

How to change extension of any file in windows 10, 8, 7 or XP
How to change, add, delete/remove extension of multiple files with/without extension Video Link:
• How to change, add, de...
How to change extension of multiple files
How to delete extension of multiple files
How to add extension of multiple files without extension