I use the sauna method when my snakes seem to be having a hard time sheding.

Basically, you take a container big enough for the snake, place paper towels on the bottom, and cover them with a thin layer of warm water. Then you place the snake inside and put the cover on (make sure you have air holes), and place it on a heating pad. Never leave the snake alone. Typically within 2 hours the shed has raised and it comes off smoothy. For my Pip his first shed was retained, and I did this method and found it easy to pull off the stuff he didn't get.