There's nothing wrong about the answer Kindofhandy wrote regarding removal of water pump pulley hardware (originally nuts--sometimes replaced by bolts) but there are easier ways to accomplish the task.
If the belt is still attached and tight you can turn the crankshaft pulley nut to get the hardware in a workable position - no need to loosen and re-tighten the belt. If the belt is loose or already off you can apply an extra large offset slip joint pliers (commonly known as "water pump pliers", coincidentally enough) around the pulley to hold it still -- or as I sometimes do, use a thin blade screw driver wedged between the studs to keep the pulley from turning while cracking the nut or bolt loose.
It goes without saying - but I'll say it anyway -- to crack the hardware loose you should only use a boxend wrench - 12 point is more positionable but 6 point gets a better grip. Use a long one to get the hardware loosened and then a short open end can be employed for turning off.
As for the OP's question about -"should I be able to turn the pulley?" - that's been answered but another possibility is that longer than required bolts have been used and are jamming against the face of the pump. -- Dave