If you buy your ticket from Telecharge or Ticketmaster, they should automatically give you a full refund of your ticket at some point.
If you bought it at the box office, I believe you have to go down before the show closes to get a refund. Otherwise, call Telecharge or Ticketmaster, depending on what site you got your ticket.
"We like to snark around here. Sometimes we actually talk about theater...but we try not to let that get in our way." - dramamama611