Once you finalize text it becomes part of the image. Therefore, there is no easy way to edit it later.
The best way to handle this type of thing in the future it to always put text on its own layer and save a copy of the PDN file before you flatten the image.
As for your problem now, I suggest going back to the original image and start again. If that's not possible, you'll probably need to remove the text using the clone/stamp tool before putting a new layer of text on the image.