On the footer of the theme you may see a link that points to the Asteroid Theme Page here on my site.

A. If you want to remove this link go change the setting on the Options Page.
Asteroid Theme -> Misc -> Remove Theme URL

Or

B. If you just want to change the link, add this code on your functions.php file. It is preferably to do this on a child theme.

function asteroid_footer_link_text($text) {
    return 'New Link';
}
add_filter('asteroid_filter_theme_credits','asteroid_footer_link_text');

replace the “New Link” with your own text or link.