I have just setup some 301 redirects in order to remove /development from the URL of my blog and wrote a handy piece of SQL to simplify 301 redirect WordPress blog htaccess. Once you have made the changes you can update your redirects /wp-admin/options-permalink.php. The reason I am redirecting to the guid which is the id based form is in case I change the slug in the future.

SELECT CONCAT('Redirect 301 ','/slugtoreplace/', post_name, ' ', guid)
  FROM wpdb.wp_posts
 WHERE post_type = 'post'
   AND post_status = 'publish';

You can then post the output from that script into your .htaccess file and everything will redirect properly.