Heh, yeah, I have a shirt that I have to re-word as well. Hopefully it will be easier to delete a listing soon. I don't think the image can be changed, because if you think about it, Amazon doesn't like it when a customer orders something and then the listing changes, etc. blah blah. You know from doing FBA. But hopefully they will at least add the ability to delete/discontinue instead of having to submit a request and wait 10 days.
T-shirt deletions are processed within 10 business days and we're working to improve the service. We will have an update to the Merch FAQ when there are changes, improvements, or revisions to the process.