I would recommend that you soak the snake and get the stuck shed off of his head--it's probably impairing his vision. There are tutorials on the site here. He's not shedding--he's already completed a shed, and the piece on his head did not come off properly, so it will need to be removed. Snakes shed all in a single piece. If pieces remain, the humidity was too low. Don't pull the stuck skin off dry, though, as that can damage the skin underneath it. It needs to be wetted down and allowed to absorb the water, then it should just peel off easily. If it doesn't, no matter what you try, then you may need to have a vet do it for you. If left in place, stuck skin can lead to skin infections, and stuck eyecaps can lead to eye infections or even blindness in the long run.
I recommend newspaper or paper towel over aspen. Once you see how much pee a ball python can produce in a single elimination, you will never want to spot clean again--gross! My snakes soak half the newspaper with one pee. I imagine that aspen soaked in pee and then dried would make for a bit of an odor, not to mention it can't be that great for their skin. Newspaper may not be as pretty as aspen, but it's really quick to change out, and it's really cheap, and much, much cleaner.
Snake cages should be odorless, so if there's a smell, something needs cleaned.