I believe it should twist right off. I would recommend using a filter wrench, like you would use for an oil filter, and twist it with that. Can always try spraying the seal with some PB Blaster or something. But as far as I am aware, it should twist off just like an oil filter would.
Just as a pointer, and I am sure you know this, but make sure you are turning filter the right way! Haha...if it is mounted correctly,while looking down at the unit, you would be spinning the filter in what appears to be a clockwise direction, but looking up at the filter from below, you would be spinning in counter-clockwise. I am sure you are doing this correctly, but have made that mistake myself before and couldn't understand why it was being such a bear to remove a simple filter!
