Toilets, Sinks, Showers, Tubs and Disposals - Shower diverter stuck

Our shower diverter is stuck in the up position. It is a Price Pfister Series 809 purchased & installed in December 1996. Is this something easy to fix? If it is, how do we fix it? I did check the Price Pfister web site but did not find any troubleshoot info on this particular problem.
Thanks!

Turn the water off (as I am sure you have already), pry the cap off the knob and remove the screw in the knob, removing it. Remove the spanner nut around the stem, and unscrew the entire bonnet, which will release the control parts. I believe you have a spring or washer that has come out of place and lodged in the ball. Purchase a rebuild kit from one of the big boxes or hardware store, and reinstall all the parts according to the directions. If you get the kit and run into a problem, please post back and we will be glad to help.

Thanks for the help Chandler! We'll give it a try!