The embedded text written in JPEG images can't be modified with a text editor, even if you use a powerful image editor because it would mean that you recreate the image in the part where is the text.
If you still want to do it then I recommend Adobe Photoshop as it's the best image manipulation tool available on the market.
You can test drive the application for a month but while you're doing it you can learn how to edit text in pictures.
