All you need to do is plug in the iPhone to your computer and let it sync. The sync will update all the back-up to the most recent information.
When you then plug a freshly restored iPhone back in iTunes will prompt you that there is a previously backed up iPhone and would you like to restore it. Doing so will bring back all of your SMS, customised homescreen, YouTube bookmarks, favourite contacts etc.
Make sure you sync the iPhone before you restore though to make sure it is the most up-to-date!! This does NOT require a jailbreak and is a feature built in by Apple, so it is safe
