Setting rpm of stepper motor per minute

Hi,
I recently started with programming my arduino and hardly know anything about it, so I hope you can help me. I try to make a stepper motor change it's RPM every minute to a value described in an array. However somehow the delay I use seems to stop the stepper motor completely. I use the CustomStepper library. Can you help me with what I'm doing wrong?
Thanks a lot!

//Copyright 2012 Igor Campos
//
//This file is part of CustomStepper.
//
//CustomStepper is free software: you can redistribute it and/or modify
//it under the terms of the GNU General Public License as published by
//the Free Software Foundation, either version 3 of the License, or
//(at your option) any later version.
//
//CustomStepper is distributed in the hope that it will be useful,
//but WITHOUT ANY WARRANTY; without even the implied warranty of
//MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
//GNU General Public License for more details.
//
//You should have received a copy of the GNU General Public License
//along with CustomStepper.  If not, see <http://www.gnu.org/licenses/>.

#include <CustomStepper.h>

//lcdschermpje
#include <LiquidCrystal.h>
  //rs op pin 12
  //rw op pin 11
  //d4,d5,d6,d7 op pin 6,7,8,9
  LiquidCrystal lcd(12,11,6,7,8,9);

//Full constructor, just the first 4 parameters are necessary, they are the pins connected to the motor,
//the others are optional, and default to the following below
//the 5th paramater is the steps sequence, where the 1st element of the array is the number of steps
//it can have a maximum of 8 steps
//the 6th parameter is the SPR (Steps Per Rotation)
//the 7th parameter is the RPM
//the 8th parameter is the rotation orientation
CustomStepper stepper(2, 3, 4, 5, (byte[]){8, B1000, B1100, B0100, B0110, B0010, B0011, B0001, B1001}, 4075.7728395, 12, CW);
//boolean rotate1 = false;
//boolean rotatedeg = false;
//boolean crotate = true;

float lut[] = {10,5,1,.5,1,2};
int i=0;

void setup()
{
  //sets the RPM
  stepper.setRPM(15);
  //sets the Steps Per Rotation, in this case it is 64 * the 283712/4455 annoying gear ratio
  //for my motor (it works with float to be able to deal with these non-integer gear ratios)
  stepper.setSPR(4075.7728395);
  lcd.begin(16, 2);
 
  // Print the message to the lcd.
  lcd.setCursor(0, 0); // First row.
  lcd.print("Volg de sterren!!!!");
  lcd.setCursor(0, 1); // First row.
  lcd.print("***************************"); 
  lcd.display();
}

void loop()
{
    float value = lut[i%6];
    stepper.setRPM(value);

    
//when a command is finished the isDone will return true, it is important to notice that
  //you can't give one command just after another since they don't block the execution, 
  //which allows the program to control multiple motors
  if (stepper.isDone() 

  )
  {
    //this method sets the direction of rotation, has 3 allowed values (CW, CCW, and STOP) 
    //clockwise and counterclockwise for the first 2
    stepper.setDirection(CCW);
    //this method sets the motor to rotate a given number of times, if you don't specify it, 
    //the motor will rotate untilyou send another command or set the direction to STOP
    stepper.rotate(1);


  }

  stepper.run();
    lcd.setCursor(0,0);
  lcd.print(value);
  lcd.display();
delay(60000);
  i++;
}
#include <CustomStepper.h>

That is not a core library. You need to provide a link.

  if (stepper.isDone() 

  )

The close paren belongs on the same line as the if statement it goes with.

However somehow the delay I use seems to stop the stepper motor completely.

]
Well, of course it does. Why is that a surprise?

Hi PaulS
thanks for the reply. the link to the library is Arduino Playground - CustomStepper .
As far as the surprise on the delay, I'm really a noob on arduino and programming. The LCD print the correct RPM so i thought this sketch might work. Do you have a suggestion for me how to achieve the change per minute without the delay?
cheers

Do you have a suggestion for me how to achieve the change per minute without the delay?

Of course. The blink without delay example shows how to do things are some time relative to another event (like the last time you changed speeds) without having to use delay().