As Dan said, sandspider, depends on what you mean by lumpy.
If it's lumpy due to grass tussocks, then maybe the topper will be able to reduce them (depending on how well established the tussocks are) with routine cutting there-after. If the tussocks are very well established, topper blades likely to need some tlc afterwards.
If lumpy means rough ground under grass, then you will need something beefier/heavier than a chain or spring-tine harrow to break it up for subsequent finer grading. Of course, as Dan suggests, running a roller over lumpy soil might do the trick when soil is soft, but not too sticky. You could try dragging a log if the ground is softish, as an experiment, but Dan is almost certainly right about this option.