Well I euthanized the most humane way i know. This is from the research i not only did on here but from other sources such as Animal Planet.
I did the lower the temp gradually method since i was told that this is the best way to do it and the fish should not feel pain.
Essentially you just add the fish to a container or bowl, cover it, and stick it in the freezer for 30 minutes. This will in turn activate all fishes instinctual response to cold weather. When the weather gets too cold for fish to be comfortable, they go to the bottom of a lake, river, or stream where they will hide. As the temp continues to drop they go into a "dormant" mode which is similar to hibernation. At this point they are effectively asleep and their vitals drop to near nothing. Once the temp falls below minimun threshold the heart finally stops.
This method of death is very similar to a human dying of exposure to the cold. You go to sleep and you never wake up.