Go To Folder

/skins/custom/_main.php:
Look For this code

<div>
<h1 id="pageTitle"><?php $Blog->disp( 'name', 'htmlbody' ) ?></h1><div><?php $Blog->disp( 'tagline', 'htmlbody' ) ?></div>
</div>

Insert at this place

Insert the code for your image like this:

Code:

<div>
<img src="img/Yourlogoname.jpg" alt="My logo" style="float:left" />
<h1 id="pageTitle"><?php $Blog->disp( 'name', 'htmlbody' ) ?></h1>
<div><?php $Blog->disp( 'tagline', 'htmlbody' ) ?></div>
</div>

Upload your image to the /skins/custom/img folder.

Make sure that you change the image Logo url name with your image name while uploading.