Hi. 1- Take a full back up (data base + public_html's folder) 2-Replace all "IPB 4.0.11" files and folders to 4.0.9, EXCEPT "conf_global.php" (be careful if you've already changed admin's folder, you must change 4.0.11's admin folder to the name) 3- Go to www.yoursite.com/admin/upgrade Good luck -------- P.S: Also it's better to disable all applications and plugins before update.