I am using Byond B54 and I want to update my 2.3.6 Gingerbread to 4.1 Jellybean .
There aren't official ways to update your phone and the only solution to this is to use the service support shop. Please, use the official webpage dedicated to this purpose.
I think you should buy branded mobile because this type of mobile are not having accessories like cover, up-gradation etc. So I prefer only branded one they do have many accessories and upgradation in every aspects.