If there is any shed encircling the body, or remaining on the tail, I would soak the snake in about 1/2" of lukewarm water. Get a small shoebox tub with a lid, add water, add snake and maybe some paper towels to add friction, put lid on, then place on the warm side of the snake's enclosure for 45 minutes to an hour. After the time is up, you can get a washcloth damp and let them slither through it. The skin should just slide right off.

You can soak them once a day for 3 days or so. Any shed that isn't on the tail or encircling the body(like a belt), you can leave until the snake sheds next time. It won't cause any harm if there are just patches of skin that won't come off. Bad shedding, especially if you just got the snake, is usually a result of the poor husbandry the snake received before you were the owner. Usually when the environment is correct, the subsequent sheds will not be a problem. That is, unless the snake is just a problem shedder anyway.

Just remember, if all the skin comes off without assistance, it's a complete shed, regardless of how many pieces the shed skin is in