Disable and delete wordpress post revisions

Add this line to your wp-config.php file (in the wordpress installation directory):
define('WP_POST_REVISIONS', false);

Run the following SQL statement to delete all post revisions; -Remember to change the <PREFIX> to whatever prefix you use in your wordpress configuration.

STOP:
Remember to backup your database before making this update.

DELETE a, b, c
FROM <PREFIX>_posts a
LEFT JOIN <PREFIX>_term_relationships b
ON a.ID = b.object_id
LEFT JOIN <PREFIX>_postmeta c
ON a.ID = c.post_id
WHERE a.post_type = 'revision';