How to set up remote system administration (ubuntu)?

Question

System administration

I installed a computer for my mother a few years ago, it has linux ubuntu on it (I won’t tell you the exact version - but it’s not less than 10.04 and not older than 12.04), package updates (without switching to a new version of the system) work automatically (perhaps this was not the best idea, although For more than five years, the computer has been working without global problems). The last time I sat at this computer was about a year ago (and my next visit is expected in the same amount of time - we live in different countries). The system works stably (if there was Windows, I would receive calls every week - before, something was constantly junk, stupid or "falling off", there is such an experience), but recently there have been questions like "how to do this?" or "how to install such a program so that ...", etc. - which makes me think about the need to organize remote access to her computer, including the possibility of administering the system. Therefore, the question is: what and how should be configured on two computers - the one that will be remotely serviced, and the one from which it will be done? Perhaps in a couple of months I will have physical access to the hard drive of the "remote" computer (my mother will come to visit us and will be able to take the hard drive with her), so if possible, please give detailed instructions on what and how should be configured on each of the computers, which programs will need to be installed (linux ubuntu will be administered, perhaps I will update the version to 16.04 lts; remote access is also expected from linux ubuntu 16.04 lts). Therefore, the question is: what and how should be configured on two computers - the one that will be remotely serviced, and the one from which it will be done? Perhaps in a couple of months I will have physical access to the hard drive of the "remote" computer (my mother will come to visit us and will be able to take the hard drive with her), so if possible, please give detailed instructions on what and how should be configured on each of the computers, which programs will need to be installed (linux ubuntu will be administered, perhaps I will update the version to 16.04 lts; remote access is also expected from linux ubuntu 16.04 lts). Therefore, the question is: what and how should be configured on two computers - the one that will be remotely serviced, and the one from which it will be done? Perhaps in a couple of months I will have physical access to the hard drive of the "remote" computer (my mother will come to visit us and will be able to take the hard drive with her), so if possible, please give detailed instructions on what and how should be configured on each of the computers, which programs will need to be installed (linux ubuntu will be administered, perhaps I will update the version to 16.04 lts; remote access is also expected from linux ubuntu 16.04 lts).

Answer 1

VNC, Chrome Remote Desktop

Answer 2

https://get.gotomypc.com
https://www.teamviewer.com/ru/

Answer 3

SSH