My motivation to access remote files of a WordPress instance/website was to change password as I could not manage to change through the easier Forgot Password option. It became apparent that you need to connect with SSH (it is one click process on Lightsail), download and configure PuTTY (for getting private key), and FileZilla (to actually get hold of the files).
In the process, I came to know about default email sending limitations on Lightsail and how to change that.
I am sharing screenshots of my own experience. I have attached relevant links for explanation.
My object to access remote files was to change password. I did this by editing functions.php file under wp-content/themes.
In the process, I came to know about outbound emails from the server being blocked by default. Here is the process I followed to remove the block:
While accessing files, you may face permission issues. For instance while I could access files in one WordPress instance via FTP, I was not allowed to edit (Connected WordPress instance on LightSail to FileZilla using SSH and could access directories and files but facing permission issues while editing). My suggestion is to seek support from Bitnami community while consulting tutorials here by Bitnami. Also, make use of WordPress.org Support as well. Stack Overflow is perhaps rigid to accept query in the first place.