Forum Moderators: not2easy
It would help if you let us know what graphics programs you have available to you. I will answer your question as best I can.
It is my understanding that you a a JPG file that you want to alter in order to use as the header for different categories in your directory.
A JPG is a flat file meaning that it does not contain different layers that can be altered. What I would do using Photoshop is create a file and copy the graphic exactly and then save it as a PSD file. You would now have a font layer within this file that contains the text that you want to modify.
Whenever you want a new header simply open this file and modify the font layer with the new text you want and then export it to a JPG using the Included Adobe ImageReady which is accessed by pushing [ctrl+alt+shift+s] together on a PC.
A better solution IMHO if indeed this is the header your are modifying is to convert it to an H1 tag and fill it with text. Or alternatively set the image as your background and write over it with HTML text formatted to your liking via CSS.
I hope that is of assistance to you,
DPG