Remember you need to swap out *all* of the chain drivetrain when you change a chain, or it will wear out the new chain faster, because it's not just the chain that wears, its' the surfaces of the sprockets and chainrings. See the images I attached to a previous post and the linked article they come from.
If those are individually interchangeable on your bike, you can change just the worn out ones, but if you actually shift gears (lots of people don't) then all of the ones you regularly use probably need to be changed.
Definitely if you can *see* wear on it, you should change it out. If you can't see the wear obviously, you may have to compare the teeth to an unused sprocket or chainring from a new set or different bike to tell.
If those are individually interchangeable on your bike, you can change just the worn out ones, but if you actually shift gears (lots of people don't) then all of the ones you regularly use probably need to be changed.
Definitely if you can *see* wear on it, you should change it out. If you can't see the wear obviously, you may have to compare the teeth to an unused sprocket or chainring from a new set or different bike to tell.