Here is the easiest way if you don't want to do it the 'right' way
http://www.wugfresh.com/
You'll need to download the LMY47Z files from
https://developers.google.com/android/nexus/images#shamulmy47z
It'll say sprint and usc only, download it anyways
Then load up wugs tool kit, enable usb debugging on your device under developer options, you'll want to 'unlock bootloader' first in wugs, then you'll want to select 'unroot and return to stock', when given the option you'll want to select the LMY47Z file you downloaded to restore from. The process will wipe your device so backup anything important first.
What I just wrote is a pretty crappy guide to using wugs, but you can Google any questions you have, use the wugs FAQ, or Google how to do it the right way with individual commands but that would take longer to type on my phone here.