A .jpg file is a raster image file, as such it contains no vector elements. You would need to reset the text in AI and place it over the existing text.
Illy is quite unable to process a raster image in such a way: to her, it is just a rectangle with inaccessible contents. If you use Live Trace, she can discern the pixels of different colours and create vector paths along transitions/changes in these colours, but that is probably of little use to you, the result being rather crude, mostly useful when a photolike appearance is desired.
Edit: Hi Larry.