This is possible. Do a mock booking on their website and it tells you how much more to upgrade to the next class. I tried and it was about $426 USD to upgrade but it is best to find out at the airport nicely, they may just upgrade you without charge, they did that for me once on the YYZ-HAV route and I did not even have status with TACA.
Purchase the next available fare family and obtain more benefits.
Brasilia to Lima Thursday, December 15, 2011, 07:03 - 09:05
Lima to Brasilia Wednesday, January 18, 2012, 22:05 - 05:35
Upgrade to ELITE
+426.00 USD (For all passenger not including taxes)