Is is possible adding Child theme?

Hi all,

Theme – Twentyeleven
Plugin – Cimy Header Image Rotator

Twentyeleven has been renamed as twentyeleven-cimy.

I expect removing the phase “Proudly powered by WordPress”. I suppose that I can delele following line on footer.php to do the job;

<div id="site-generator">
				<?php do_action( 'twentyeleven_credits' ); ?>
				<a href="<?php echo esc_url( __( 'https://www.ads-software.com/', 'twentyeleven' ) ); ?>" title="<?php esc_attr_e( 'Semantic Personal Publishing Platform', 'twentyeleven' ); ?>" rel="generator"><?php printf( __( 'Proudly powered by %s', 'twentyeleven' ), 'WordPress' ); ?></a>
			</div>

However on upgrade WordPress I’ll lose all changes. Can I do it by adding a child theme? If YES please advise how? Pointer would be appreciated. Thanks

Rgds
satimis