low rpm

Hi I am controlling the stepper motor speed with potentiometer but i am not getting low rpm.I want rpm range from 2 to 100 please can any one help me with this without losing torque of motor

The program that you posted looks OK to me.

Did you read this before posting a programming question ?

@jack13978, how can you expect advice without posting your code?
And please use the code button </> so your code looks like this and is easy to copy to a text editor

Stepper Motor Basics
Simple Stepper Code