wp-docs

Edit the file called “YourWordPressFolder/wp-admin/includes/post.php”

Look for the code below (should start around line 517) wp(”post_type=post&what_to_show=posts$post_status_q&posts_per_page=15
&order=$order&orderby=$orderby”);

Change $posts_per_page to whatever you wish.

The default value for $posts_per_page is 15.