Robin, yes, you can fix a picture after it is approved.
You will need to adjust your image in photoshop, or whatever program you are using.
Save fixed image to your computer.
Then upload the new image to GCU.
Next click on the old dark image and you will see the option under the keywords that states "Change Image" and click on the Change Image option
Then it will take you to another screen and you will see that same "Change Image" option under your photo.
Click on the second "Change Image" option and it will take you to the area where you uploaded your new photo.
Click on your new image and press save.
That should do it.
Hope that helps.
Sher