Hi Steven,
There is a hole in the back to pop the cover. The wheel is then held in position by a large phillips screw if I remember correctly. I have rounded the sharp end of an old phillips screw driver, then gave it a 90* bend about an inch or so from the rounded end. Find the hole in the back, I think there might be two, stick the 90 degree bend into the hole and pop the cover off.
Regards
Chris