Per the thread title ... there doesn't appear to be a way to delete an old profile image and/or upload a new one to replace it.
EDIT: Nevermind ...
-- When logged in and viewing "Home -> User Profile Image," select "Admin Editor Options -> New Editor" from the yellow hover dropdown menu.
-- Browse and select a new image to replace the existing profile image.
-- Selecting "Submit Changes" at the bottom of the page returns the message: "You replaced an image but you will have to FLUSH YOUR BROWSER CACHE to be able to see changes to the image."
-- The new User Profile Image should display after refreshing with CTRL-F5 (or similar browser command) to flush the cache. For some reason, this took three or four attempts for the replacement image to display. The first few attempts resulted in an error message something to the effect of "You don't have permission to delete the User Profile Image" (yes, I was logged in ...)
Anyway, moving right along.