Reflashing nexus 5 because of unstability/bootloops

So my brother gave me his nexus 5 because it bootloops, i got it to work for some time, but its still very unstable, so id like to flash the origional firmware on it, as a form of reset, any help? im new on the nexus 5 forum XD

(btw it restarts after a camera error)

Thanks! :fingers-crossed:

from xda-developers http://ift.tt/298n524
via IFTTT