You can remove root but it isn't as simple as a setting in the phone. The link I gave you is something that is super simple to flash it is one of the less complicated mods. You should at least read the stickies and pay attention to the parts about using twrp or cwm.
You would place said file on the sd card in a location you can navigate to again, turn the phone off, press and hold volume up and the home key then press the power button until you feel the phone vibrate at which point you can release all three keys. This has now placed you into recovery mode if you have the stock Samsung 3e recovery(it will mention something about 3e in the very top line of that screen if it is) you will not be able to flash that file. Use the volume keys to navigate to highlight "reboot phone" Then press the power key And you will be back to using the phone as you have come to know it.
If you have cwm or twrp custom recovery you would select "by touching the appropriate tab" apply update.zip, then proceed to navigate to where your file is stored on the external SD card, follow the prompts, reboot the phone and your phone now works as it should.
To unroot the only way I know off the top of my head is going to be difficult at the least and would not give you official software on 4.3 because AT&T has no love for us guys anymore.
As far as tethering I found most apps very subjective before 4.3 and on lock down afterwards, that link by enewman17 made it so that the stock app works awesome and one isn't even required to pay said service provider for services that should be free to begin with. It rewrites a few lines in the tethering app so it doesn't look for subscriptions or authorization it just does what it was designed to do.
Whatever you choose do some research first it isn't that scary playing inside the phones but with this 4.3 make sure absolutely certain you do not flash a bootloader that is pre4.3 you won't like the outcome(it is fixable but intensive) and use common sense if it wasn't made for your exact phone model don't use it.
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