The hotels have money exchange if you need to cash USD into THB, but the hotels profit from rates given (i.e. less than normal). The total will be in THB and you can pay via CC or cash. I usually do the cash route in Thailand.

Go to the nearest bank, they are everywhere, or a cash exchange booth anywhere on the street. They give near to at the actual rate and charge 20 BHT and an additional 5 BHT per full transaction. Use high bills, get better rate. Others use ATMs, I don't.