Hey you can do this by editing your theme’s (twenty twelve) content.php (create child theme its very important).
Note that I am not very good at php. So do it at your own risk.
find this in content.php:
<?php the_post_thumbnail(); ?>
remove it. Than find this code:
<a>" title="<?php echo esc_attr( sprintf( __( 'Permalink to %s', 'twentytwelve' ), the_title_attribute( 'echo=0' ) ) ); ?>" rel="bookmark"><?php the_title(); ?></a>
And change it to:
<a>" title="<?php echo esc_attr( sprintf( __( 'Permalink to %s', 'twentytwelve' ), the_title_attribute( 'echo=0' ) ) ); ?>" rel="bookmark"><?php the_post_thumbnail(); ?><?php the_title(); ?></a>
You can see here that it have added:
<?php the_post_thumbnail(); ?
before:
<?php the_title(); ?>
in <a href="permalink"> </a>
If it don’t work for you or you are having issues than please notify us.
[Please post code & markup between backticks or use the code button. Your posted code HAS been permanently damaged by the forum’s parser.]