Rewrite author URL

This is the standard author archive slug and it’s independent from the theme code. Tbh I’m not sure if you can replace the username especially because the username is unique whereas two or more users can have the same author name. That said (after a quick search) I didn’t find a way to replace the username but I found following thread: http://wordpress.stackexchange.com/questions/4241/override-default-url-for-author-pages – maybe it helps you (or your programmer/coder) and you can use it as a starting point.

Update – I also found: http://wordpress.stackexchange.com/questions/5742/change-the-author-slug-from-username-to-nickname which maybe answers your question – but I didn’t test it.