const int red = 3;
const int ylw = 2;
const int grn = 1;
const int btnUp = 4;
const int btnDwn = 5;
int up, dwn;
int mode = 1;

void clear() {
  digitalWrite(red, 0);
  digitalWrite(ylw, 0);
  digitalWrite(grn, 0);
}

void setup() {
  pinMode(red, OUTPUT);
  pinMode(ylw, OUTPUT);
  pinMode(grn, OUTPUT);
  pinMode(btnUp, INPUT);
  pinMode(btnDwn, INPUT);
  clear();
}

void loop() {
  up = digitalRead(btnUp);
  dwn = digitalRead(btnDwn);

  if (up == 1) { 
    mode++;

    if (mode > 3) { mode = 1; }

    //delay(500);
  }

  if (dwn == 1) {
    mode--;

    if (mode < 1) { mode = 3; }

    //delay(500);
  }

  digitalWrite((mode-1), 0);
  digitalWrite(mode, 1);
}