The factory instructions tell you to "carefully pry them apart by starting at the spindle opening". However, I've always turned the grease injector port screw in a few turns after I remove the two screws that hold the pedal halves together to create a gap at the opening, and then use a pen knife with a narrow blade or a very thin putty knife to separate the halves.

Detailed instructions are here.
http://www.speedplay.com/pubs/Frog_I...1.14.08web.pdf