You can make the basic changes like passenger’s name, departure or arrival date, and destinations within 24 hours of the flight departure. However, if you have basic economy fare tickets then the time limit to make changes is up to 24 hours of booking time only. 

We do change or plans sometimes and the very first thing we do is to cancel our flights. If you have a basic economy fare ticket then you can cancel your flight within 24 hours of booking time. Because basic economy fare tickets are non-refundable after 24 hours of risk-free period. Check out the process to cancel a non-refundable and refundable/flex ticket Delta Flight Change