Uploading any sketch will delete any previous sketch stored in the memory. A sketch must always include the functions setup() and loop(), but they can be left empty in this case.

Just copy and paste the code below or load the example in the Arduino IDE: File > Examples > Basics > BareMinimum. Read more about the example here.

void setup() {
  // put your setup code here, to run once:

}

void loop() {
  // put your main code here, to run repeatedly:

}