Originally posted by chrism24 I just bought a 645z with 55mm F2.8 lens.
Generally when you hear a solid click, that means it is now locked on. When you hear a softer click, it is now released and should come off.
If it doesn't, then it was put on incorrectly or slightly askew and may take a bit more force than you'd prefer. If having to use a lot of torque, you may want to remove the lens from the camera so as not to possibly damage the lens mount.
The PH-RBN 67mm petal type hood is not cheap and I understand your apprehension, but it's useless backwards.
Pentax PH-RBN67 Lens Hood 38768 B&H Photo Video
And sometimes another pair of hands will just have the right touch to remove it. Better to ask someone mechanically minded for a try and not the professional jar opener in the house. This is a brains not brawn situation.