How to update rooted S3 to 4.3 using only OTA? I unrooted my phone to get OTA update but while updating in the boot screen, it stopped at around 25% with the red triangle and the Android bot then reboots automatically. 

I have tried many times with no luck. 

How should I go about this?
Since rooting changes the system image, the OTA update won't apply. You need to download the ROM (e.g. from sammobile.com) and flash it by hand (using Kies).