add_filter('asp_search_phrase_before_cleaning', 'asp_replace_characters', 10, 1);
add_filter('asp_query_args', 'asp_replace_characters', 10, 1);
function asp_replace_characters( $s ) {
$characters = "',._-?!"; // Type characters one after another
$replace_with = ' '; // Replace them with this (space by default)
if ( isset($s['s']) && !$s['_ajax_search'] )
$s['s'] = str_replace(str_split($characters), $replace_with, $s['s']);
$s = str_replace(str_split($characters), $replace_with, $s);