yes iv been rooted my s4 before but now i unroot it .. but i cannot update my device anymore to 4.3 since my device is 4.2 right now... any advice will be fine and appreciated
1. Go to backup and reset on your S4. The phone will reboot back to stock.
2. Use ODIN to flash the stock recovery for your S4. After it flashes and reboots the device modified message will not appear and you can then update without a problem.