In a terminal, type:
sudo su
To access a root-level prompt. Then, run:
crontab -e
To begin editing your crontab, a table of tasks to run automatically at a given time. It will open in your preferred text editor. Modify it to include the following lines:
0 7 * * 1 apt-get update && sudo apt-get upgrade -y
To automatically update and upgrade your apps at 7AM every Sunday. Read-up on crontab to see how to adjust to your liking.