When logged in as an Administrator, there is no method to delete one of the other administrators (such as an individual who left the company). The delete/trash can icon within Settings > Editor is disabled and grayed-out for all administrators. I can only delete a Content Editor. There is also no method to convert a Content Editor into an Administrator, or to invite someone to become an Administrator.
Here is my site Read-Only: LINK
(how to share your site Read-Only link)