The show in Sao Paulo, Brasil on April 6th has been moved from Morumbi Stadium to Arena Anhembi. Details on how to exchange your tickets are posted at the Live Pass website (English).
(Thanks Rafael, Antonio and Pablo)
Update (March 21st, 2013): Not surprisingly, this change is not going over well with many fans - "I’ve just read the comments at the XYZ fb page, and EVERYONE is furious! Lots of fans giving up on attending the
show.. meanwhile Santiago, Lima and Buenos Aires are close to sold out.. shame
on us! And now things are going from bad to worse here.. the whole SP show thing is
already with the customer justice.. if you have the chance, translate this link (English)" (Thanks Antonio)
Update (March 22nd, 2013): New info about the ticket exchange from Live Pass. Looks like there will NOT be an additional charge. All info here (English). (Thanks Burton_)