This can be done by entering the website irctc.co.in....U need not login....in home page itself there is a link for cancelling counter ticket....First u have to cancel ticket online just using ur PNR number and later u hav to collect the refund at PRS counters...This suits for the person who is not able to go to PRS counters and the person who is cancelling at last minute ie few hours before Charting....!! See the image attached....!!