The page you are looking at is being generated dynamically by CodeIgniter.
If you are exploring CodeIgniter for the very first time, you should start by reading the User Guide.
If you would like to edit this page you'll find it located at:
application/modules/welcome/views/welcome_message.php
The corresponding controller for this page is found at:
application/modules/welcome/controllers/welcome.php
This section is injected by calling a module controller, like this:
<?php
echo Modules::run('welcome/hmvc/module_run');
?>
This section is loaded using module partials, like this:
$this->template->
load_module_partial('partials',
'welcome/hmvc/section_partial');