mobile

Hello,
I cannot update my Xperia Z1 (C6902) from Andoid 4.4.2 to Android 5.0. The update was available for me since day before yesterday. I have downloaded the OTA 3 times. When I try to install it, the phone restarts and I can see the Android logo and a loading bar. However, after 15 seconds or so, the installation fails and the mobile phone restarts to the Android 4.4.2. On restarts, it says that the update failed and please download again. I also tried updating my phone via PC (I am using Windows 7 64-bit) using Sony Companion. Still, no luck. Sony companion detects the phone, tells me that there is an update available. I selected the option to update my phone. It asked me to disconnect the phone. I dissconnected the phone. It connects to the Internet and downloads something, probably Sony Update Engine. However, if I remember correctly, when it downloads the update package, it shows the size and time remaining. It did not show the time or the size. That means that it did not download the update package. After downloading the Sony Update Engine, it says that it is preparing my PC for the update (there is no more download going on). After preparing the PC, the Update Application is terminated. How do I solve this problem?