Forgot Wifi Help??

For some reason the other day my computer would not connect to wifi automaticly like it always does, and when i went to put in the password it did not work. I am thinking that I have forgotten my password because it did not work. I can connect using an ethernet cable, like i am right now, but that is a pain becasue I want to you wifi. Please let me know if you can help me. I have an airport extreme

thanks