How to repent of a bad emotion?

Life happens, and you realize you're not reacting well. You're upset when you shouldn't be, or frustrated over nothing (or what should be nothing).

What do you do?

I suspect it is not enough to say to yourself "I shouldn't feel this way, so I won't." It is good to perceive you shouldn't feel this way, but emotions don't turn off just because you decide to stop feeling them. I think the way to proceed is to say to God, "I shouldn't feel this way, but I do. Help me." This expresses our reliance upon God, rather than assuming we can independently control our feelings.