Remove or change powered by in Footer
open footer.php
change this code:
<p><a href="https://www.appthemes.com/themes/classipress/" target="_blank" rel="nofollow">ClassiPress Theme</a> - <?php _e( 'Powered by', APP_TD ); ?> <a href="https://wordpress.org/" target="_blank" rel="nofollow">WordPress</a></p>
with this( with image-must be uploaded in your wordpress you need copy link of image):
<p><a href="http://www.online-shop.rs/" target="_blank" rel="nofollow">Besplatni oglasi</a> - <?php _e( 'Sponzor', APP_TD ); ?> <a href="http://radimo.rs/" target="_blank" rel="nofollow"><img src="http://radimo.rs/
wp-content/uploads/2017/01/logo.png" alt="uuuzzz" width="180" height="45" /></a></p>
Links and title you can change and write what you want its just a sample with logo image
with this( without image):
<p><a href="http://www.online-shop.rs/" target="_blank" rel="nofollow">Besplatni oglasi</a> - <?php _e( 'Powered by', APP_TD ); ?> <a href="http://radimo.rs/" target="_blank" rel="nofollow">Oglasi za posao</a></p>