Step motor rotating speed

Hi,
I looking for way to change rotation speed, to increase rotating speed of step motor.
Sketch bellow work fine but I have not possibility to controll speed.
What should I do?

#define step_pin 3    // Define pin 3 as the steps pin
#define dir_pin 2    // Define pin 2 as the direction pin
#define MS1 5     // Define pin 5 as "MS1"
#define MS2 4       // Define pin 4 as "MS2"
#define button1 7
#define button2 8


int direction;    // Variable to determine the sense of the motor
int steps = 500;      // Number of steps that you want to execute (for full steps, 200 = 1 turn)

void setup() {
   pinMode(MS1, OUTPUT);     // Configures "MS1" as output
   pinMode(MS2, OUTPUT);     // Configures "MS2" as output
   pinMode(dir_pin, OUTPUT);    // Configures "dir_pin" as output
   pinMode(step_pin, OUTPUT);    // Configures "step_pin" as output
   
   pinMode(button1, INPUT_PULLUP);
   pinMode(button2, INPUT_PULLUP);
   digitalWrite(MS1, HIGH );      // Configures the steps division (see above)
   digitalWrite(MS2,  HIGH);    // Configures the steps division (see above)
   digitalWrite(dir_pin, LOW);   // Sense (HIGH = anti-clockwise / LOW = clockwise) - It can be also changed
   
 
 
  stepper.setMaxSpeed(3000);
  stepper.setAcceleration(1000);

}

void loop() { 

   if (digitalRead(button1) == LOW || digitalRead(button2) == LOW) { // ako ni jedan taster nije pritisnut
  digitalWrite(step_pin, LOW);
  digitalWrite(step_pin, LOW);
   }
  
  
 if (digitalRead(button1) == LOW && digitalRead(button2) == HIGH) { // ako je taster 1 idle, a taster 2 pritisnut
    digitalWrite(dir_pin, LOW); // move in the LOW direction
    digitalWrite(step_pin, LOW);
    delay(3);
    digitalWrite(step_pin, HIGH);
    delay(3);
    
  } else if (digitalRead(button1) == HIGH && digitalRead(button2) == LOW) { // ako je taster 2 idle, a taster 1 pritisnut
    digitalWrite(dir_pin, HIGH); // move in HIGH direction
    digitalWrite(step_pin, LOW);
    delay(3);
    digitalWrite(step_pin, HIGH);
    delay(3);
  }
  
  
}

Your sketch doesn't compile:

sketch_apr03a.ino: In function 'void setup()':
sketch_apr03a:26: error: 'stepper' was not declared in this scope
'stepper' was not declared in this scope

Have a look at this Simple Stepper Code

The standard Stepper library is not intended for stepper drivers that take step and direction signals. Either write your own code or use the AccelStepper library.

...R
Stepper Motor Basics