Point of order: that's a multispeed freewheel, not a casette. Not trying to nitpick, just want to make sure you get the right tool, which is in fact the FR-2 as posted above. Don't be surprised if it takes some pretty righteous torque to get it off off there, and it may make an unsettling noise as it breaks loose. You will need a breaker bar or a big ol' wrench, don't bother if all you have is a set of channel lock pliers.
Also, you can't really take apart the freewheel to service it. The teeth look fine, and don't be alarmed if it sounds like there is something rattling around inside.