GALAXY S3 update from Ice Cream Sandwich (4.0.4) to Jelly Bean (4.1.1)

[tambo_04b]

How can i update my S3 from 4.0.4 to 4.1.1?

The "check for updates" always show no updates available.

AP: I9300XXBLFB

CP: I9300XXLFB

CSC: I9300OJVBLF3

 

[Kevinpleasants]

after opening about phone and choosing software update are you pressing on Check New at the bottom?
go to settings, about phone, software update then choose Check New.