I favor debit cards over credit cards, a worry that was expressed above.
Cash, not too much, is fine. There are "Casas de Cambio" all around.
Check a few to see what the going rate is, and then choose one. Banco Santa Cruz, Vimenca (Western Union) are major players in the money exchange market, so they usually give you a fair deal. NEVER, EVER change money in the street.
As additional advice, photocopy your docs and leave the real ones in a save place, like a hotel safe or your room safe.
Have fun, be wise,
Merry Christmas,
HB