How can I update my Android KitKat 4.4.4 to Lollipop on mobile data?

Ok, there are two ways in which you can update your device to Android 5 Lollipop from Android 4.4.4 Kitkat.

Option 1:

Go to settings > About > Software update > Uncheck "Update via WiFi only".
Continue with the download and install process.

This should start downloading the update files.

Option 2:

If the above procedure didn't work, try this.
1. Go to google, search for the OTA update (Over-the-air) file for your model, eg, <lollipop ota for X, x is your phone model>
You should be able to download the OTA files easily.
2. Install a custom recovery on your phone. (TWRP is recommended)
TeamWin - TWRP
https://twrp.me

3. Boot into recovery.
4. Clear cache/dalvik cache.
5. Install the .zip file from the recovery.
6. Reboot the phone, and it will be booted into Android Lollipop.