The password is stored in your login keyring.
The easiest way to find it is with GNOME Seahorse.
Install Seahorse from AppCenter.
Open the application from AppCenter or open the Passwords and Keys application from the Applications Menu.
Click the Login bookmark on the left under Passwords.
Find your login which should be marked as a Network password.
Updates are provided by the repositories available on your system. The safety depends on multiple factors, a proper summary can be found here:
It's not a dumb question. If the updates were done through the App Store, it would be fine. You could also update using the command line console
(this is the command)
sudo apt update && sudo apt upgrade
Hope this helps you.
There's a lot of content in this "question" so it's hard to fully understand what you're asking. It's often better to ask a succinct question if you want a succint answer, but I'll try and answer some of your points.
In summary, if you have forgotten your password, it's not just installing software you're going to struggle with. Changing certain ...