Though we are quick to try to roll a bumpy lawn, this will cause long-term soil damage. If the bumpiness is due to patches of incompatible species of coarse, bunch grasses like tall fescue or orchardgrass growing in a stand of predominantly Kentucky bluegrass or perennial ryegrass, apply Roundup to kill the coarse grass and reseed.
Most lawns are bumpy because of improper establishment, followed by natural settling of the soil.
Professionals will apply thin layers of sand or soil over finely manicured turf and then use modified brooms to move the topdressing down to the soil surface. This topdressing will eventually help to smooth out minor undulations over many years while not harming the turf plants. If the lawn is in really bad shape, it is better to start over. The settling part of the process is regularly overlooked, thus resulting in eventual undulations.