You can do it easily. You must follow the steps below.:-
1) Click Appearance tab in your WordPress admin panel.
2) Click on editor link.
3) Now, open header.php by which you can edit the header.php file.
4) Now find the code shown below :
<title><?php wp_title(”); ?><?php if(wp_title(”, false)) { echo ‘ |’; } ?> <?php bloginfo(‘name’); ?></title>
and replace it with code like <div>< img src=”enter the url of the image which you want to add as your blog logo”/></div>
Hope this helped you!