You're not gonna get the fixed cup out without a few swear words and a wrench the length of your leg. Plus it likely has left-hand threads, so you were probably tightening it (exceptions: Swiss and Italian BB's- find out what kind it is before trying to remove it). Most people leave it in there, just clean and re-grease it from the adjustable side. That being said, cotters are soft and easily drilled out if you can't hammer them out- usually it takes a single stiff blow on the top of the loosened nut to pop out the cotter. Or maybe your co-op has a cotter press. More than likely it will destroy the cotters; they'll need replacing anyway. If you use the hammer method, make sure to support the axle/crank on something so you don't dent the axle and cups with the ball bearings when you whale on it with the hammer- then you'd really need to take the cup out (to replace the ruined BB).