Wondering how to fix our "old lawn"? It is so lumpy and bumpy...It is hard to not twist your ankle while mowing.
Kent County Michigan
Sounds like you may be talking a major lawn refurbishment. A tall task and time consuming, a decision that will require your constant attention. Three basic tenets, you have to water it, you have to feed it and you have to maintain it correctly (mowing). Within each category, there is a myriad of detail. Scrimp on any of the three and you will have less than optimum growth. "Lumpy and bumpy" if that's all you're concerned about could in itself be a major project, depending on the severity. Tilling, leveling and reseeding is one option. Spreading top soil over the top of the existing lawn, leveling and then reseeding is another.
Otherwise, you can read some of what is involved in basically creating a new lawn here: http://msue.anr.msu.edu/resources/establishing_a_new_lawn_using_seed_e2910