You can only get an 'update' if the phone shows an available 'update' in the phone's "Settings". If nothing is showing there, then that device has not be set up to get it from the manufacturer. You would have to ask them as to why.
Getting the OS any other way (through say rooting the device) then would not be an update but instead would be forcing a new/different OS on a device that may or may not be able to handle it. Not a fan of rooting myself, to easy to brick a device. Should you have questions about rooting, I suggest you post in the "Rooting, Jailbreaking & Unlocking" forum.
http/www.tomsguide.com/forum/forum-117.html