Thanks for the prompt replies.
I am using DRV8825 stepper motor driver, high current for driving the stepper motor. Pololu - DRV8825 Stepper Motor Driver Carrier, High Current
I have attached the picture. I am using Pololu - Stepper Motor: Unipolar/Bipolar, 200 Steps/Rev, 57×56mm, 7.4V, 1 A/Phase stepper motor. It has six leads and I am using for of them as mentioned on the website.