why my galaxy s3 won't update?

[yu na]

hello i am person who using galaxy s3(at&t). i am having problem with update my soft ware. i know there is 4.3 version and my phone is 4.1 version
to update software, i go to setting on my phone and find about device;software update;check for updates;press 'ok'
and it say"current software is up to date you may check again in24hours. why my phone is doing this stupid thing? anyone know?
please tell me how to update my software.helllllllp me