LG G3 D855 only rooted, I want to unroot update and root again

I've rooted some months ago my D855, I rooted it only because I want to write on the SD and use some software that requires root. Since 1 month my G3 says to me that there is a google patch that increase the usability. I'd like to update, but when I try to do this it says to me that rooted devices cannot be updated.
Then I'd like to unroot my device, update, and then root it again, but I'd like to do this without miss my data. How can I do? Some hint?

help me to root and unroot micromax s300 step by step

frendz pls help me to root and unroot micromax s300 step by step...i tryed many apps for rooting micromax s300 ..but no results...pls help me.....battery life is also very poor in my handset....

unroot & full back to stock

Hello
I am new to LG G3
I am preparing my self to root my phone
I wonder, is there some LG method to track user modification on this phone like Samsung do? (and then you have to run TriangleAway to clear it)
or is it simply to use unroot method and wipe phone, and I can be sure that my phone will be ok in front of LG support / service
Regards
Michal