Well, a steel cup in an aluminum frame may suffer from galvanic bonding. As a Cannondale, it will have left the factory with English threads, so clockwise to loosen the fixed cup. The best tools, as noted above, are the Campagnolo or VAR fixed cup tools (not the home mechanic stamped ones, but the solid, shop-quality ones), but also as @Salamandrine noted, most people, and even many shops these days, do not have them. The Sheldon Brown universal fixed cup tool is quite effective, given sufficient leverage, and not difficult or expensive to fabricate:

Tool Tips--Bottom Bracket Cups


But if there's nothing wrong with the cup there's no compelling reason to remove it. Leave it in place, and put off the chore of removing it until you need to replace the entire bottom bracket. Which, with regular maintenance, may never happen.