"do I have to cancel today" makes me think this was purchased less than 24 hours ago.
Like Adam said, if the fare has a change fee, any form of credit will forfeit that fee.
If it's been more than 24 hours, there's no benefit in cancelling until either:
a) You hit a schedule change or IRROPS that let you do it for free, or
b) 2 hours before departure, while you continue to hope for a)