How could remove an element of a list by number?

I tried this to add a1 gameobject or remove it and it’s OK but how could I remove a gameObjcet only with element number?

         if (Input.GetKeyDown (KeyCode.J)) {
		myList.Add (a1);
	     }

           if (Input.GetKeyDown (KeyCode.N)) {
		myList.Remove (a1 );

	}

If the list has 5 elements how could I remove for example element 3?

The list class has a method called RemoveAt which does what you want:

myList.RemoveAt(index);