Answer: Probably the easiest solution is to spread top soil over the lumpy parts and then overseed the entire lawn. Usually a lawn gets lumpy when the soil becomes compacted. To help avoid this in the future you can rent an aerator (sometimes called a plugger) which will remove one inch wide by three inch long plugs of soil from your lawn. If you leave the plugs on the lawn they will disintegrate with water from the sprinkler and the soil will work it's way down into the ground. Aeration should be done every 3-4 years to keep the lawn area from becoming lumpy.
Best wishes with your lawn.
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