The foreign currencies that exchange at the best rates are US dollars, British pounds, or Euros. Traveler's checks may also be exchanged, but typically at lower rates and not at all Forex Bureaus. Forex Bureaus can be found throughout Accra, and many of the larger hotels in Accra have their own. Reliable places to exchange your money become less common outside of Accra, so it is best to get enough cedis to tide you over during your time outside the city. Many Forex Bureaus will give you a better exchange rate for larger denominations of US dollars ($100s and $50s). 

Most banks in Ghana have ATMs where you can withdraw money in cedis. Call your bank before leaving home to make sure your ATM card will work and to find out if you need a separate pin number.  

It's important not to use credit cards to pay for things unless it's absolutely necessary. Credit card fraud is fairly common. If you need to use a credit card, make sure the transaction is processed in front of you. Keep an eye out for any unusual transactions on your account.