To use the package manager (
apt) on the Demo image, you'll need to change your timezone.
First, you'll need to locate the correct timezone file at
/usr/share/zoneinfo. There should be a folder for your country and a file in that folder for the closest city to you.
$ rm -f /etc/localtime$ ln -sf /usr/share/zoneinfo/<country>/<city> /etc/localtime
For example, if you're in Central Time USA, you'd use the following commands:
$ rm -f /etc/localtime$ ln -sf /usr/share/zoneinfo/America/Chicago /etc/localtime
Now, you can run
sudo apt update and
sudo apt upgrade to get your system up to date.