Remove footer text in the wordpress blog

Thanks for your reply . But i need to know to create the custom function to remove the footer in the blog.

Yes Your Idea to create the child theme is good .But i expect that i need the functions to remove those footer message.

For example:

<?php
function copyright() {
echo "this is the footer message";
}
add_action('wp_footer','copyright');
?>

I need to add the footer in the wp_footer hook ,I need if any other hook to remove the footer message.