How to access terminal if removing the UI (Homebridge as Synology package)?
When updating a plugin, I get an error message I have not seen before:

The user "homebridge" does not have write access to the target directory:

/usr/local/lib/node_modules

I see that a tip is to remove the Homebridge UI and reinstalling, using two terminal commands. 

But I am terrified of messing up Homebridge for me, as I really don't understand how to access terminal outside of the graphical UI. If I understand how this works correctly, once I uninstall the UI plugin, I must go elsewhere to reinstall it, but where? Not having Homebridge in Docker, I don't where the terminal resides that can affect Homebridge.

I am most likely very stupid in not figuring this out, but I hope someone can help?

I should also say that I have tried to run sudo commands in the terminal window in the graphical UI, but whenever I am asked for the password, the admin password I use for logging into Homebridge is not accepted. This is another concern.