Q: How do I differentiate when I need to change the starter vs replacing the starter relay?

Sometimes when trying to start the car, I will hear a click and the car won't start. Sequential attempts end in the same result. Only after several attempts, or if I turn off all power and wait a minute, it will then start.

I've been told that I need to change the starter, while someone else advised that I can just change the relay. How do I know which I need to change?

My car has 115000 miles.
My car has an automatic transmission.