Edit username/password field 'help text.'

Searched all over for this in my php theme files and all over the admin interface.

when clicking, Account settings > manage fields

Where can I edit the help text for the username/password field? Currently there is help text being generated on hover of the input field, displaying in a black box. Is there anyway to change the behavior of this within Drupal without having to modify tpl.php files?

Unlike created fields, there is no ‘edit’ button next to these default fields. (username/password)

Drupal version: 

Source: https://www.drupal.org/taxonomy/term/3/feed