Board Thread:Support Requests - Getting Started/@comment-26285531-20161003030403/@comment-26437440-20161003050855

You used to be able to change both the image and description through Special:Promote, but that got discontinued a couple years back and they've been pretty quiet on its replacement.

You can contact staff and ask them to change it, but no guarantee that they will. Last time I asked it couldn't be done due to an error or something.