If it's one of the ones with a plastic ring that turns and adjusts height we've recommended using heat to at least 4 or 5 people that had ones that were stuck and all of them were successful. at getting it to turn. A hair dryer like Stick suggests will work given some time. If you use a heat gun use it on low power so that you don't damage the plastic. If that isn't the problem then a photo would help and you can post one from your own hard drive by using the Go Advanced post option.
