Each time you revise a blog post, WordPress saves a copy so that you can go back and restore older revisions (or see the changes that different editors have made). However, these post revisions take up space and can impact the speed of your site.
If you'd like to limit the number of revisions, you can add the following line to your wp-config.php file:
define( 'WP_POST_REVISIONS', 3 );
You'll see a section toward the bottom of the file that includes other define() clauses. Just add the code above on a new line, save the file, and upload it via SFTP if that's how you're updating, and you're all set!
If you have a ton of revisions on older posts, we recommend using the plugin WP Sweep to clean those up.