It is great news that you were able to get tickets for such a popular show!
When a show is that popular, it happens that an extra date is added to accomodate all fans wishing to attend. We understand that you would like to exchange the tickets you are holding for better ones on the new date. However, such an exchange is not possible - the promotors and ticketing agencies have agreed on that rule.
We wish you a good time at the concert!