This is to remove any ROM you've installed, un-root and re-lock your bootloader. I'll also post a link to reset your flash counter if you've tripped it.
Basically I'm just going to post a few links to guides that are already here.
-First is to backup:
Backup literally everything on your phone and external sd card just to be safe. Just imagine that if you lost your phone what you would've wanted backed up. (I'm not saying you're going to mess up your phone, just that the internal sd card will be wiped clean. Pics, settings, videos, etc... all wiped off the internal card. Backup up your ext is just to have your bases 100% covered, none of this process actually uses your ext card. You can just remove it if you'd like also.
-Second, Check your Flash counter:
More than likely unless you've been flashing custom stuff through Odin you haven't tripped it. In otherwords if you haven't used Odin or just rooted your phone using Odin and then flashed everything else in CWM or TWRP, you haven't tripped it.
To check your flash counter you need to enter download mode - 'Vol down+Home button+Power button'
You will need to be in download mode for the next step anyways, so just doublecheck the counter first.
If you have tripped it, use this app from the play store Triangle Away
-Third is to flash the stock rooted image via Odin:(This image version will re-lock your bootloader and un root you)
Go to section #5 of this Guide and follow the instructions. Use the UN rooted official version and Just to clarify, there is really only ONE option to choose if you plan on returning your phone to Verizon.(Official VRALG1 4.0.4)
(Shortcut to the file if you are familiar and already have Odin, Here)
-Lastly, perform a wipe via recovery just for safety's sake:
Hold 'Volume up+Home button+Power' from your phone being power off. And do this BEFORE you boot up the stock version otherwise you could get stuck in a bootloop and have to do a battery pull.
It's that simple and this will leave your phone in an "out of the box" state therefor safe to return to Verizon without them catching on.