Although I have the S3 and have personally unrooted it, I would surmise your S4 would be similar.
So, I searched around a little and came across this:
How to Unroot the Samsung Galaxy S4 (Verizon) - TheUnlockr
Which seems to be the same procedure to unroot my device.
Basically, it will have you flash the stock firmware via ODIN. (a program that is run on the computer while the phone in plugged in and in download mode) There are download links there for the stock firmware and ODIN.
Now, before you do that, wait for other confirmations from those who have your device
Since being rooted have you flashed any roms or kernels?
By the way, what issues are you having?