You wanna go to your header.php and chage the part that says:
<?php
if ( 'true' == $wpnj_distinction_options['display_header_flames'] ) { // Enabled by default ?>
<img src="<?php echo get_template_directory_uri(); ?>/images/lt-flurl.png" alt="wispy image" /><a href="<?php echo home_url( '/' ); ?>" title="<?php echo esc_attr( get_bloginfo( 'name', 'display' ) ); ?>" rel="home"><?php bloginfo( 'name' ); ?></a><img src="<?php echo get_template_directory_uri(); ?>/images/rt-flurl.png" alt="wispy image" />
<?php }else{ ?>
<a href="<?php echo home_url( '/' ); ?>" title="<?php echo esc_attr( get_bloginfo( 'name', 'display' ) ); ?>" rel="home"><?php bloginfo( 'name' ); ?></a>
<?php } ?>
To say <img src="link to your image" href="<?php echo home_url( '/' ); ?>" title="<?php echo esc_attr( get_bloginfo( 'name', 'display' ) ); ?>" rel="home"<?php bloginfo( 'name' ); ?>
Please do keep a backup of header.php before you edit it