Code to remove default WordPress post meta boxes. Add to functions.php file. Taken from http://wpmu.org/remove-wordpress-meta-boxes/

Remove WP Post Meta Boxes

// REMOVE POST META BOXES
function remove_my_post_metaboxes() {
remove_meta_box( 'authordiv','post','normal' ); // Author Metabox
remove_meta_box( 'commentstatusdiv','post','normal' ); // Comments Status Metabox
remove_meta_box( 'commentsdiv','post','normal' ); // Comments Metabox
remove_meta_box( 'postcustom','post','normal' ); // Custom Fields Metabox
remove_meta_box( 'postexcerpt','post','normal' ); // Excerpt Metabox
remove_meta_box( 'revisionsdiv','post','normal' ); // Revisions Metabox
remove_meta_box( 'slugdiv','post','normal' ); // Slug Metabox
remove_meta_box( 'trackbacksdiv','post','normal' ); // Trackback Metabox
remove_meta_box( 'categorydiv','post','normal' ); // Categories Metabox
remove_meta_box( 'formatdiv','post','normal' ); // Formats Metabox
remove_meta_box( 'postimagediv','post','normal' ); // Featured Image Metabox
remove_meta_box( 'submitdiv','post','normal' ); // Categories Metabox
remove_meta_box( 'tagsdiv-post_tag','post','normal' ); // Tags Metabox
}
add_action('admin_menu','remove_my_post_metaboxes');