Yes remove the plastic cover over the belt, loosen the bolt on the idle pulley on the idler with 9/16" wrench, use a prybar to push the idle down to tighten the belt.
There should be a pointer on the idler that points at 1 oclock when there is no tension on it and points to 3 when the spring is wound up. This point often falls off after 1500 to 2000 hrs though and may just be spinning around where ever it wants.
You really should download the book if you can. You should also remove the idler if you have time, remove the cover in the center on the front side and make sure it still has grease inside. My got dry in there and wore the brass bushing out of the center.
Here http://www.skidsteerforum.com/DesktopDefault.aspx?tabid=54&frmView=ShowPost&PostID=4139
is the thread on what happened when mine lost its grease inside.
Skidsteer.ca