Agents are listed by publish date. Most recent are listed first. Change publish date to change order.

To change order in code and make agents go alphabetically, go to agents_list.php

Instead of

$args = array(
'cache_results' => false,
'post_type' => 'estate_agent',
'paged' => $paged,
'posts_per_page' => 10 );

Add 2 more options: orderby and order

$args = array(
'cache_results' => false,
'post_type' => 'estate_agent',
'paged' => $paged,
'posts_per_page' => 10 ,
'orderby' => 'title',
'order' => 'ASC' );