Search on the Internet for a free currency converter tool and input the amount of British Pounds you have and select the U.S. Dollar to get an approximate conversion amount.
Call the headquarters branch of your local bank and inquire if they perform currency conversions from pounds to dollars. Not all banks do currency conversions, and definitely not at all branches. Verify any fees required by the bank to process the transaction. Prepare to show identification in any transaction.
Contact a reputable travel agency or AAA office for assistance in converting pounds to dollars. There is always a fee at locations like this, especially if there is no other option nearby. Ask to see the current currency conversion sheet prior to performing any transactions to ensure a fair change.
Visit an international airport and ask at any on site banks or currency conversion kiosks if they can change Pounds to dollars and what fees or limits are involved.