How to access postgresql.conf file?

Question

PostgreSQL

Hello!
The task is to edit postgresql.conf to open access for external connections. The database is on my computer. Problem - the main folder does not open (it is /var/lib/postgresql/9.5/main).
In the info about the folder: the owner is Postgresql administrator, and for the group "postgres" and "others" - access is denied.
You can make a dump of the desired database and solve my problem through it, but I would like to figure out how to open the main folder, I ask for your help.