Location of the update script: https://jabbalaci.github.io/teaching-... . Direct link: https://jabbalaci.github.io/teaching-... .
Links:
https://wiki.ubuntu.com/Releases
https://www.virtualbox.org/
https://www.ubuntu.com/
http://distrowatch.com/ (popularity of Linux distributions)
Minor correction: in the video I say Ubuntu 16.04 is supported until the end of 2021, while the deadline of the support is April 2021.