int ledsNum[4] = {2, 3, 4, 5};
int led = 0;

void setup() {
 for(int i = 0; i < 4; i++) {
  pinMode(i, OUTPUT); // D2, D3, D4, D5 - output
 }
}

void loop() {
  led = (led + 1) % 4; // led value always from 0 to 3

  digitalWrite(ledsNum[led], HIGH);

  for(int i = 0; i < 4; i++) {
    if (i != led) {
      digitalWrite(ledsNum[i], LOW);
    } 
 }
 delay(200);
}