XperiCheck.com pretends to be every Sony Xperia device known, and asks the Sony servers for any updates for that device. It then stores any new information it finds, and for which device, and makes it available for everyone to see.
The XDA-Developers forum is the best place for that, this guide should generally work and there are lots of experts to help you troubleshoot.
This site is not owned or endorsed by Sony, it has no affiliation with Sony at all. You should follow their press releases to see when your device will get an update.
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