How to restore stock ROM I am on a Samsung Galaxy S4. I bought it used, and it came with Team Win Recovery Project installed.

My simple question is - how can I remove TWRP, and restore the stock ROM?

I am not experienced with rooting or messing around with the back end of Android, so please keep that in mind when responding.
I can not assure you the method would work or not but after browsing all over I found this satisfying post, hope it will help you too! 

http://www.androidsage.com/2016/02/03/restore-samsung-galaxy-s4-to-stock-lollipop-firmware/

Try it on your own risk :)