so, for example, here:
<?php
$users = get_sub_field('author');
echo get_avatar( get_the_author_meta( 'user_email' , $users['ID']), apply_filters( 'twentyeleven_author_bio_avatar_size', 120 ) );
?>
Once you have the user array you just need to use that array element wherever the WP function calls for the user ID. Or you can do this
$user_id = $users['ID'];
and then use that variable wherever you need to supply the user ID.