Change file extension name

Easy Step

• Go to my computer/ Tools/ Folder option/ Veiw

• Uncheck(hide extension for known file types)

• Click Apply Then OK

Now you should be able to see the file extension:

 Right-click the file name and select Rename (or left-click and hold down the button for one second). Enter the new extension like so:

After entering the new extension, hit the Enter (return) key. Windows will give you a warning that the file may not work properly. This is quite safe—remember that you can restore the original extension if anything goes wrong.
It's also possible that you might get another message telling you that the file is "read-only". In this case either say yes to turning off read-only, or right-click the file, select Properties and uncheck the Read-only box.
If you do not have permission to change the file extension, you may have to login as Administrator. Another option is to make a copy of the file, rename the copy and then delete the original.
Note: Windows treats file extensions as case-insensitive, i.e. .RTF is the same as .rtf. However other operating systems do not, and will treat MyDocument.RTF and MyDocument.rtf as two different files. Therefore it is good practice to always treat your files as case-sensitive for maximum compatibility. This is especially crucial if you are going to use the files on the Internet. We recommend that you get into the habit of using all lower-case letters for all file extensions—then there's no confusion.