If you want to delete the autosaved post revisions on your wordpress blog manually from phpmyadmin using sql query instead of trying out plugins, follow these steps ( assuming that you have access to your website’s control panel / phpmyadmin or mysql manager ):
Step 1: Log into your server and goto phpMyAdmin
Step 2: Select your database from the list of databases on the left side
Step 3: Click on SQL tab to open the sql query box page.
Step 4: Type this query in the sql box and press Go button (press confirm again on next page once you submit this query)
DELETE a,b,c FROM wp_posts a LEFT JOIN wp_term_relationships b ON (a.ID=b.object_id) LEFT JOIN wp_postmeta c ON (a.ID=c.post_id) WHERE a.post_type='revision';
This will delete all wordpress posts revisions from all the posts including all their meta data.