Determine whether you will plant a fresh batch of cool-season grasses or warm-season grasses. Cool-season grasses---as their name suggests---thrive in the colder months. Warm-season grasses thrive well in warmer weather. Your seed choice will determine when you should plant your new seeds. Start planting warm-season seeds in early spring, and plant cool-season seeds in early fall.
Kill your old grass with herbicides. Spray the herbicides directly on the grass. Avoid spraying anything you don't want to die (e.g., trees, shrubs and flowers). Start the extermination of the old grass early because it may take a few weeks for the herbicides to fully work. Read the instructions on the herbicide containers carefully before you use them.
Upturn the top 6 inches of soil in your yard. Use a shovel for small areas. Larger areas of lawn may require a rototiller. A rototiller is a machine specifically designed to break up soil. Break up any clumps of soil larger than your fist.
Pour your grass seeds into a hand-pushed seed spreader. Move the seed spreader to the corner of the yard and start pushing it at a slow and steady pace. Walk in a zigzagging line through your yard, spreading the seeds evenly over the upturned soil.
Spread a thin layer of topsoil over the freshly planted seeds. This helps protect them from hungry birds and other animals that might try to eat your seeds. Water the lawn with a gentle spray of water.