WordPress Default theme Twenty Thirteen and other shows Proudly Powered By WordPress at the end . It is highly recommended that you do not remove this link but if you really want to remove this here is tip how to:

The location of powered by WordPres is in the footer.php file  at site info div  of wordpress twenty thirteen theme. Remove this block of code :

<div>
<?php do_action( ‘twentythirteen_credits’ ); ?>
<a href=”<?php echo esc_url( __( ‘http://wordpress.org/’, ‘twentythirteen’ ) ); ?>” title=”<?php esc_attr_e( ‘Semantic Personal Publishing Platform’, ‘twentythirteen’ ); ?>”><?php printf( __( ‘Proudly powered by %s’, ‘twentythirteen’ ), ‘WordPress’ ); ?></a>
</div><!– .site-info –>

The footer.php  page  of theme is generally located at  wordpress root folder/wp-content/themes/twentythirteen/

You can also edit the page from there  or from
wordpress dashboard > appearance > editor
search  for footer (footer.php) from right panel

Removal of  above code  removes Proudly Powered By WordPress in your theme