Changing date format in monthly archive in Views
Create a template file of your view Display output: views-view--view-post-by-date--block.tpl.php

Make some slight changes where row is printing in your tempalate file: 

         &lt;?php if ($rows): ?&gt;
        &lt;div class="view-content"&gt;
         &lt;?php 
   $output = '';
 for($i=0;$i&lt;5;$i++){
$filter_link = date("Ym",strtotime("-$i months"));
$filter_display = date("Y F",strtotime("-$i months"));
$link = $GLOBALS['base_url'].'/post-by-date/'.$filter_link;
 $output .= '&lt;a href="'.$link.'"&gt;'.$filter_display.'&lt;/a&gt;('.count($filter_display).')&lt;br&gt;';

  }
print $output;
// print $rows; ?&gt;

 &lt;/div&gt;