You can rent a slice seeder at most tool rental places. It's a walk
behind, gas powered machine that slices grooves in the soil and drops
the seed in them which gives good germination. It's the best way to
overseed any larger size areas or to establish a new lawn.

Like Peter advised, it's too late this season to do this. In your
area, the best time would be early Sept. If you can make it through
another season, I'd wait till then. If you try to do it in spring,
make sure you start as early as possible. It's more difficult because
you will have weeds to compete with, require more water, and there is
less time for the grass to become established before hot, dry weather.

Another thing you want to decide is whether what is there is worth
keeping. For example, if what you have is a grass that is rougher than
you would like, disease prone, etc., then the solution is to kill the
whole thing with Roundup about a week before reseeding it. Once you
start on a project like this, it's not that much more work. You want
the best grass seed you can find, preferably one that is endophyte
enhanced.