in sidebar.php in wp-contents/theme/default, its this code
<li><h2>Meta</h2>
<ul>
<?php wp_register(); ?>
<li><?php wp_loginout(); ?></li>
<li><a href="https://validator.w3.org/check/referer" title="This page validates as XHTML 1.0 Transitional">Valid <abbr title="eXtensible HyperText Markup Language">XHTML</abbr></a></li>
<li><a href="https://gmpg.org/xfn/"><abbr title="XHTML Friends Network">XFN</abbr></a></li>
<li><a href="https://www.ads-software.com/" title="Powered by WordPress, state-of-the-art semantic personal publishing platform.">WordPress</a></li>
<?php wp_meta(); ?>
</ul>
</li>
Be aware that when WordPress upgrades, it overwrites the default theme. If you customize the default theme its best to duplicate it in a new folder that has a different name, within the theme folder. Also change the name of the customized theme, at the top of style.css in the new folder, as this is where WP gets the name of themes from.