I selected what you said from the synaptic package manager, ticked the boxes, installed, ran the two updates you mentioned, restarted, and still no brightness function. Did I miss anything or can you tell me some other way?
Install the backlight one first and check it works.
You can install the others too but do them one at a time as there have been reposrts of the notebook slowing down so if you do then one at a time, you can uninstall anything that causes problems.
The LXDE desktop environment is not the most user friendly, its designed to be very light on resource, so some feature aren't as simple as other desktops, I would suggest Linux Mint, Zorin or Ubuntu.