How do I unroot my g4? h81120i

I rooted my device but want to unroot it so I can return it as it is broken. How do I do this? It's not bricked or anything the screen is just cracked. I followed this guide if it matters: http://ift.tt/1QsMdwY

If possible can you give me specific and detailed easy to understand instructions? I don't know what flashing ROM means.

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