Hi, and welcome.
Updates from carriers do not always roll out for every phone, so while the current version is Jellybean 4.3, that does not mean that your phone will get updated.
If you are adventurous (and not squeamish about voiding your phone's warranty) you can join forums, find your phone's folder, and look for the "all things root" section. In there, you will find instructions on rooting and updating your phone. Just be careful and make sure you read and understand everything before you begin. Ask questions--folks on forums are always willing to help.