Good advice above. Just be sure not to be too forceful. Apply enough pressure that the snake has to work to slither through but don't squeeze so tight that it can't move at all. It probably won't come off the first time through, because it will take a couple of times for the moisture of the paper towel or cloth to loosen the skin.
Also, if it is just a very small part of the tail tip that didn't come off you may not have any problems in the future. Sometimes they just don't have a perfect shed and the very next time they do. It's always a good idea to have an idea of how humid the air is in the viv. A cheap hygrometer from the pet store will help with that. That way if you ever have a humidty problem you will know before the next shed.
Good luck