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 Monday. Read-up on crontab to see how to adjust to your liking.