Hello and welcome to Android Forums. Hopefully I can help you with your problem.
If your device and carrier are offering that update, your device should receive a update notification. You can go into settings and check for a firmware update too.
If the 4.3 update isn't available for your device through your carrier, it is possible that you can root your device and install a ROM with that version.
Please note that rooting your device will void its warranty.
If you have any other questions regarding your device, I invite you to join Android Forums. We have many sections for specific devices which contain a wealth of information.