PartitionMagic CANNOT read a Mac partition. The most practical way to do what you want is to clone your Windows partition (using whatever tool you like, including DriveImage which is made by the same people that made PartitionMagic), then use the Boot Camp Utility to un-partition the drive. That will leave you with one big partition with OS X on it. Now use Boot Camp Utility again to make a larger partition than you had before, and restore that cloned image onto it. Not "quick and easy," but it's not a major hassle either.