1- Go to

http://yourwordpressdomain/wp-admin/theme-editor.php

2- Then select the theme you are using (ex: xx), and click on Header header.php link (You will edit the file wp-content > themes >xx>header.php)

3- (Backup your header.php first) then replace the tag <title></title> with the following code:

<title><?php wp_title(”); if(wp_title(‘ ‘, false)) { ?> | <?php } bloginfo(‘name’); ?></title>

<title><?php if (is_home()) {bloginfo(‘name’) ;} else { wp_title(‘ ‘);} ?></title>