I had some pedals stuck on my conversion, they were rusted, bent, and only had grips on one side, the other was smooooooth, and I had to remember to flip each pedal over if I ever took my foot off.
I tried a pedal wrench, then some WD-40 and let it soak.
Then I took a wrench, and my trusty cheater bar (an old Steal mountain bike flat bar) and gave it a bit of torque (Just remember that one side will be reverse threaded!!!) and they came right off.
make sure you clean off the threads before putting on new pedals! Nothing ruins a crankset like stripped threads