How to change post thumbnail title and alt attributes to post title?

Look at this
http://codex.wordpress.org/Function_Reference/the_post_thumbnail

second argument in this function you can set a few set fields, such as alt, title, source and class:

$default_attr = array(
        'src'   => $src,
        'class' => "attachment-$size",
        'alt'   => trim(strip_tags( wp_postmeta->_wp_attachment_image_alt )),
        'title' => trim(strip_tags( $attachment->post_title )),
    );