I don't really know of a quicker way to do this, but my guess would be to create a new template based on one of the other templates within the folder (try "page" or "single"). Find the image location (it may be in the "header", in which case, copy "header.php" and rename it to "singleheader.php", you may have to call it differently in your new template.
You then upoload it, go to wordpress, and change the template of the about page to your new template (it's somewhere in the left bar).
Somebody could explain it a lot better than me though. Here's a relevant page in the codex
Pages « WordPress Codex