Warnings are removed by moderators if they see that you've changed in attitude.
This means that if you make constructive posts, help out here and there ( not back seat moderating ), etc, then someone will notice and remove it. Obviously if you stagnate on the same level *glances at a4yo*, or don't post at all, it won't happen.
I wouldn't worry about it though: with one warning, if you don't make screw ups, you're safe. It's not like people will treat you differently here because of it.