tutorial on downloading files from server in order to update iOS app content

I'm a novice iOS app developer. I want to learn a different, probably better way to update the content in my apps.

Currently, when I have new content, I open the Xcode app project, type new content over old content, upload to App Store, and release it as an updated version.

But better apps in my field (medical quick-reference, my day job is a physician) have an "update content" button within the app. When clicked, the app reaches out to a server, gets new content as one or several files (I imagine), plugs it in where it belongs, and then carries on. No new coding in Xcode, no updated app gets uploaded.

How might I do this? How can I have a button press go find a file on a server, pull it into the file structure of my iOS app (file structure that I know nothing about but I'm willing to learn), and deliver new content to my physician users?

I'm having trouble finding this info because search terms like "upload file" or "update app" (and similar) think I'm searching for help on how to build an app update in Xcode and send it off to Apple. I've searched for guidance but I keep getting the wrong kind of guidance because I can't think of good search terms. Now that you see what I'm driving at, I'm hoping people will point me in the right direction.