Software updates are released by the mobile network of the device as well as the device manufacturer.
It normally goes like this:
- Google release a new Android version.
- Manufacturers take this new Android version and modify it to work on their devices.
- Manufacturers test the version, and push it out to unlocked devices first via desktop software update and then via OTA update if available.
- Mobile networks/Carriers then take the Android version modified by the Manufacturer and modify it themselves to add carrier specific apps/features.
- Carriers pass it onto the manufacturer to release to the public [OR] carriers release it to the public via their custom OTA app.
As such, it can take some time to get the update, however I would advise you check using the desktop program if there is one.