How to return to stock Android after installing Ubuntu Touch

Whenever I try and uncompress the tar file, I get this:

tar (child): nakasi-jro03d-factory-e102ba72.tg: Cannot open: No such file or directory
tar (child): Error is not recoverable: exiting now
tar: Child returned status 2
tar: Error is not recoverable: exiting now

I'm fairly new to Ubuntu. So I'm pretty sure that's my fault. So I just compress it manually using the GUI. But when I try to flash it, I get

sudo: ./flash-all.sh: command not found

First, place your Nexus into fastboot mode. To do this, turn the nexus off, and then turn it back on while holding the volume down button. You should see a green android guy in the center. Plug this into your laptop/desktop via USB.

Now, run these commands in a terminal one at a time:

wget https://dl.google.com/dl/android/aosp/nakasi-jro03d-factory-e102ba72.tgz
tar zxvf nakasi-jro03d-factory-e102ba72.tgz
cd nakasi-jro03d/
sudo ./flash-all.sh

This should do the trick.