You have to remove the pump, it's a tight fit getting the 3 or 4, (I can't remember for sure), 1/4" bolts that hold the pump out. You should be able to fit a 1/4" ratchet on them and if not a small 1/4" wrench.
There is an allen screw that holds the pump impeller to the motor shaft. Sometimes it can be a problem to get the impeller to slide off the motor shaft, (especially if the pump seal has been leaking any - from your picture, yours looks pretty good and should hopefully slide right off). Don't pull on the pump body when trying to remove it from the motor shaft, wedge a pry bar on the top edge of the impeller and lever it down and off the motor shaft, (you don't want to bind the carbon/ceramic face seals and crack or mess them up or you will have a water leak at the pump impeller seal).
Before removing the spring from the idler pulley arm, mark the notch that it is in. They have an adjustment template to tell what spring slot the spring should be put in but I can't remember if it comes with the new belt or with the pump seal and impeller kit.
Here's the part link to the belt ==> http://www.repaircli...5303280326/3235
And here're some purdy-pitcher previews of where you'll be working:
Belt and Idler Pulley detail: