You've not explained why you want rid of the existing grass. There's
seldom any good reason to. Without yet hearing why, the most likely
options is to add soil where wanted & seed. Repeated mowing is all it
takes to remove almost all non-grasses.

My old college had wonderful lawns. When asked what the secret was,
the
gardeners would say "Just give it a close trim twice a week, every
week
mind, and after 200 years it looks like this."

That's humour of course.

Only to the extent that very few people manage such a council of
perfection with a domestic lawn. But I have read that if you close-mow
a lawn frequently, and at least once a week, preferably more often,
the coarse grasses and weeds will eventually give up and you'll be
left with a very clean lawn after a few months or so.

Agreed. My landscape gardener told me many moons ago that grass likes
being cut, but weeds don't. I just mow regularly and they eventually
disappear.

I believe it is an evolution thing. Grass grows from the bottom, which
is why they survive grazing herbivores better than broad-leaf plants,
which grow from the top.

That sounds about right.