Hi monikad,
The "Powered by WordPress" part is hard-coded in the theme template file, specifically lines 64 and 65 of footer.php:
<?php _e(' Powered by ', 'busi_prof'); ?>
<a href="<?php echo esc_url( __( 'http://wordpress.org/', 'busi_prof' ) ); ?>"><?php _e('WordPress', 'busi_prof'); ?></a>Simply remove those two lines and edit the copyright text in the theme's footer customization menu to your liking.
Hope that helps.