When I open system update option then it show blank screen what I do?
First, check if the phone is connected to internet(wifi or mobile data operator).
Restart your phone.
If problem persist,make a factory reset(but you will loose all your personal data,so backup them first).
To factory reset your phone go to settings,backup and restore and hit Factory reset.
Wait and check again Update menu.If problem persist,go to Repair Center to reinstall software.
All the best!
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