By mistake I have selected Mr instead of Ms in the name of person. So how to change it? I have e-ticket of it booked on IRCTE.
The general answer to this is phone the booking company (or airline directly) and be prepared to pay an admin charge. Do not leave this to the last minute as you often can't change within a window before the flight (and having tried to do this in the airport before I know that doesn't always work ...). Note that sometimes it isn't possible at all.
The specific answer can be found on IRCTC FAQ here: http://air.irctc.co.in/flights_faqs.html
Can I change my reservation (name, date and time changes)?
Customer can contact the toll free number of the call centre for any change on the booking. Customer can also call the airline for rescheduling your journey i.e. change of date time, travel etc. also. Changes to your booking might attract a flight change fee and the applicable fare difference, and this can be done through the airline. However changing of a passenger's name is not possible.
Now, I think they mean you can't change the name directly with the airline, but can with the booking service (although I suspect most airlines will change the name, but maybe only the booking service can prove that you are who booked the ticket).
This is the Customer Support number (from the same page):
We offer 24x7 customer support. You can call us at 1800 110 139 You can also write to our customer support team at email@example.com someone will get back to you within 12 hours of your inquiry.
I'd be interested to know how you get on, since that FAQ answer is a bit contradictory.