When an update to Android is released, it takes a lot of time for the update to reach each device, as there are multiple and device specific versions of Android in the market.
This is annoying if you want to check some new feature in the new version, but when you check the Check for system updates settings, its not available for you yet!
Fortunately, there is a way to force Android to get system updates. To always be in the queue, and get the update as soon as its available, dial *#*#checkin#*#*. Note that your must use your device number instead of checkin while dialing.
This will make sure that you get the updates as soon as they are released.