Originally Posted by BAWTH
I followed and used this thread ( http://forum.xda-developers.com/show....php?t=1963790 ) to root my phone, and i have no troubles following the steps. I searched around the thread and found out that i can unroot my phone with the SuperSU app, so i went into the app and selected the unroot button. To my knowledge it worked, since when i went into my Root Check app it said that there wasn't any root found. But here is my problem, when i go into my phone settings and select the stock update for my phone it gives me a message of "Your device has been modified. Software updates are not available", so am I missing something? Is there another step i must do to be able to update my phone from 4.1.2. My phone is the Galaxy S3 SGH-I747M. Thanks for taking the time to read my post!
Try doing 2 things: First do a hard wipe/reset from settings (after backing up your data, of course). Then boot into download mode and see what your settings are especially if you have a custom or official binary. Sometimes though OTA update availability may take 24-48 hours to register. Finally, if you really want to update your phone to the latest OS, this could be done manually and I'd be glad to point you in the direction of this. Since you are still on 4.1.2, I would suggest you take the opportunity to free unlock your phone on 4.1.1 (if you haven't done this already).