Add it to functions.php

/**
 * Remove a top level admin menu in Dashboard
 *
 * http://codex.wordpress.org/Function_Reference/remove_menu_page
 */
function remove_menus(){
 
  remove_menu_page( 'edit.php' );                   //Posts
  remove_menu_page( 'edit-comments.php' );          //Comments
  remove_menu_page( 'tools.php' );                  //Tools
 
}
add_action( 'admin_menu', 'remove_menus' );