Sony has started rolling out the Android 6.0 Marshmallow update to its Xperia C5 Ultra smartphone. Carrying a firmware number of 29.2.B.0.122, the update is currently hitting the device's Dual variant (with model number E5533) in Italy. As is usually the case with OTA roll outs, it may take some time for the update to hit your device. Meanwhile, if you feel impatient, you can manually check for the update by heading to your handset's Settings menu. Via
Source: http://www.gsmarena.com/sony_xperia_c5_ultra_dual_starts_receiving_marshmallow_update-news-20564.php