How can I change the speed of a stepper motor?
Do you understand how a stepper works?  You send it pulses and it steps for each pulse you send it.  The faster you send the pulses the faster it will run.  The slower you send the pulses the slower it will run.  You have lines in your code like this:

void StepForwardDefault()
{
  Serial.println("Moving forward at default step mode.");
  digitalWrite(dir, LOW); //Pull direction pin low to move "forward"
  for(x= 1; x&lt;4000; x++)  //Loop the forward stepping enough times for motion to be visible
  {
    digitalWrite(stp,HIGH); //Trigger one step forward
    delay(1);
    digitalWrite(stp,LOW); //Pull step pin low so it can be triggered again
    delay(1);
  }
  Serial.println("Enter new option");
  Serial.println();
}


Can you see the part that is sending HIGH and LOW to your step pin?  See the delay that is determining how fast those pulses go out?  Can you imagine how you might change that delay so that the pulses go out faster or slower?  Here's a hint, delay works in milliseconds, but if you want to go faster than this then you'll need to work in microseconds.  Can you find the version of delay that works in microseconds in the Arduino reference?