Hey there,
You would either need to edit the code directly to remove the PHP or you could hide it with some CSS:
.dateview{display:none;}
There is a parent container with a class of mediumfont but this is also used on the 404 page so I didn’t target it.
If you wish to create a child theme and remove the PHP so it doesn’t load at all then there are 3 files:
content-single.php
<?php if(is_single()) { ?>
<div class="mediumfont">
<div class="dateview">
Written by <a rel="author" href="<?php echo get_author_posts_url( get_the_author_meta( 'ID' ) ); ?>"><?php the_author() ?></a>
on <?php the_time('F j, Y'); ?> <?php edit_post_link( __( 'Edit', 'cleanblack' ), '<span class="edit-link">(', ')</span>' ); ?></div></div><div style="clear:both;"></div><?php } ?>
image.php
<div class="mediumfont"><div class="dateview">Uploaded by <a rel="author" href="<?php echo get_author_posts_url( get_the_author_meta( 'ID' ) ); ?>"><?php the_author() ?></a>
<?php edit_post_link( __( 'Edit', 'cleanblack' ), '<span class="edit-link">', '</span>' ); ?></div></div><div style="clear:both;"></div>
loop.php
<div class="mediumfont"><div class="dateview">Written by <a rel="author" href="<?php echo get_author_posts_url( get_the_author_meta( 'ID' ) ); ?>"><?php the_author() ?></a> on <?php the_time('F j, Y'); ?></div><div style="clear:both;"></div></div>
Hope this helps.
Take care.