The Jelly Bean update bumps up the software version of the Xperia T to 91.A.0.489 and brings improvements in the camera application, lock screen and dialer. You should also expect smoother performance of your device, courtesy of ‘Project Butter’.
Users reported updating via Sony’s PC Companion app, but the update is not yet up for all countries as the UK for example still hasn’t gotten it. It should arrive soon, though.
source: Xperia Blog