Can't save settings.txt changes.

Hi all,
We are switching from Zen4 to Zen 7, and starting to do testing. When we setup a pc initially, we have a test IP assigned to it. then when we go to deploy it to one of the other buildings on campus, We need to change the IP address to one that is on that subnet. However, the changes that we are making to settings.txt are not staying when we reboot the pc.
With Zen4, the settings.txt was located in /sbin.... now it isn't. I'm finding it in the root. I'm guessing that this is a copy, and not the actual file I need to be updating..... Would one of you please point me in the right direction....
Thanks in advance,
Mark Waters
Michigan State