Step 1:
Please open "My Bookings".
Step 2:
Then select the ticket you want to cancel using "Check Trip Details" button
Step 3:
At the bottom, Click on "Cancel ticket" button. And please check the refund calculator before cancelling.
Step 4:
After the cancellation, It will take upto 15 days to get refund in your account. However 15 days is maximum time, you may get at the earliest.