You can exchange foreign currency at Mexico City´s airport 24 hours a day, or at any bank in Cuernavaca between 9:00 a.m. and 4:00 p.m. (Monday - Friday) and 9:00 a.m. to 2:00 p.m. (Saturday).
ATM machines are also available at the airport and throughout Cuernavaca. They charge a small fee for the service. It's as safe to use an ATM card in Mexico as it is in the U.S. or Europe. When withdrawing money, just be aware of your surroundings, don't let strangers assist you or distract you, and be sure to put your money safely away before you go back out onto the street.
Most major credit cards are widely accepted in Mexican stores, restaurants and hotels. It's a good idea to make a photocopy of your credit cards and write down the numbers to call in case you lose your cards or have some problem using them while you're in Mexico.
We recommend that you not carry large amounts of cash on you when you go out to explore the city. Just take what you think you will spend, and keep the rest of your money locked in your suitcase or in a safe place in your room.