How to keep my Live Ubuntu 14.04 LTS update?

Hi there. Please help me with the following issue: how to keep my Live Ubuntu 14.04 LTS update?
I tried the advice bellow and the result was disastrous: after security update was done, when I booted again, the screen turned out black and said it has error and could not open.

http://askubuntu.com/questions/194/how-can-i-install-just-security-updates-from-the-command-line#412:
Install security updates only
apt-get -s dist-upgrade | grep "^Inst" |
    grep -i securi | awk -F " " {'print $2'} |
    xargs apt-get install

So I had to reformat the USB and start all over from the scratch: download Ubuntu, install it on USB, configure Browser, install all my software, etc.

Now I set up “Software and updates to “download automatically” updates, but how I can check is it actually doing something – to see what has been updated and when.
And is it tha all really so simple or I am missing something? Please help?