int leds[6] = {13,12,11,10,9,8};
int button = 7;

void setup() {
  // put your setup code here, to run once:
  for(int i = 0; i < 6; i++){
    pinMode(leds[i], OUTPUT);
  }
  pinMode(button, INPUT);
}

void loop() {
  // put your main code here, to run repeatedly:
  int i = 0;
  while (i >= 0 && i < 6){
    digitalWrite(leds[i], HIGH);
    delay(500);
    digitalWrite(leds[i], LOW);
    i = (digitalRead(button) == HIGH) ? i - 1 : i + 1;
  }  
}