Here’s the answer for where to replace code:
Go to:
> Appearance > Editor
> Open “Main Index Template (index.php)”
Find:
<img src="<?php $key="thumbnail"; echo get_post_meta($post->ID, $key, true); ?>" alt="<?php the_title(); ?>" />
Replace the above full line of code with the following:
<img alt="" src="<?php if ( p75HasThumbnail($post->ID) ) { echo p75GetThumbnail($post->ID, 150, 150); } ; ?>" style="float:left;margin:0 5px 0 0;" border="0" />
Thumbnail Size Editing:
If you want a different size thumbnail, change 150, 150 to your desired width and height.
As a precautionary note:
I would first comment out the first line of code you find to this: <!--img src="<?php $key="thumbnail"; echo get_post_meta($post->ID, $key, true); ?>" alt="<?php the_title(); ?>" /-->
so that if it doesn’t work you can always revert. Commenting out code is just that, it hides the code from the browser. You can then place the new line of code below or before the commented out line.
Best wishes everyone!