Kill the Grass
Since renovation basically starts from scratch, the first step is to kill all the existing grass and weeds in your lawn with a burndown herbicide such as RoundUpä which kills their roots too. It is "nonselective," which means it kills virtually any plant it is sprayed on. However, it breaks down quickly in the soil into harmless components.
About 10 days to two weeks prior to the scheduled lawn renovation, spray the herbicide over the turf area that is to be replaced. Choose a calm day to avoid damaging nearby plantings from spray drift. Use a compression sprayer that allows you to direct the spray close to the surface of the lawn.
Mow Short and Remove Debris
After 10 days to 2 weeks the old lawn will be dead or dying and you can prepare a seedbed. Remove as much of the dead turf as you can by setting your lawn mower as low as it will go and collecting the debris with its bagging attachment or with a blower vacuum. Then, go over the entire lawn with a garden rake to get up as much debris as you can to expose the soil between dead grass stubble for better seed contact. Grass will not germinate unless it directly contacts soil.
Aerating and Topdressing (Optional)
One of the disadvantages of renovating by seeding a new lawn over existing dead turf is that it is difficult to upgrade the soil as well. Taking time to aerate the soil with a lawn core aerator after you have raked up all the debris and before spreading seed will introduce more air into it. This greatly improves the soil’s quality and reduces compaction so the new grass roots can penetrate it easily. Don’t rake up the cores. Just leave them to break down in the rain.
Increase the fertility and texture of the soil by sprinkling some seed starting fertilizer and/or a ½ inch layer of Canadian sphagnum peat moss over the turf as a topdressing before sowing the grass seed. If you have already aerated they will fall down into the air holes and mix with the existing soil.