Using WordPress to edit existing content

Forgive me, I’m completely new to this. I’ve been given the task of maintaining/updating some of the existing content on a client website (their IT guy bailed and left them hung out to dry). WordPress is already set up and functioning on their server. I would like to use the WordPress installation I just installed on my PC to access and add/modify the content on that server. How can I configure my WordPress installation to access the existing information on the client’s server and make the edits/additions I’ve been tasked with? All the documentation I’ve seen has to do with new/fresh installs; I doubt the client wants me to install WordPress a second time on their machine.

Thank you in advance.