[AC Question]

my friend put a root on my samsung galaxy s4 in attempts in trying to unlock the network.. wich was unseccesful. i am still on a bell network.
i did factory data reset on my device thinking that would delete anything he changed but when i go to software upgrade it tell me that it cannot complete that action because my device is modified.

[Rukbat]

1) To change the network, you need a SIM card from the new carrier and you need the unlock code for that particular handset - each S4 has a different unlock code. Rooting has nothing to do with it.

2) If the ROM has ever been rooted, the update should fail. You can do things while rooted, remove root, and a stock update will still brick the phone. You'll have to reflash a stock ROM. See [Samsung] How to flash Stock ROM via ODIN. You can probably find a ROM file at SamMobile Firmwares. No matter which carrier you're using, it's a Bell phone, so flash a Bell ROM.

3) There's no need to know which method he used to flash the new ROM. If you want to root the phone again, after the update, it depends on the version you update to. (Google keeps patching the exploits used to root the ROM, and people keep finding new exploits, so you have to use a rooting method that works on that phone running that version of Android. An S4 4.3 root program won't work on the same S4 running 4.4.2.)

4) Tell your friend to stick to things he knows. Android phones aren't on his knowledge list yet.