The lawn on our back garden slopes from left to right. Over the years it has had ponds removed, flower beds removed and extra turf added. This has resulted in it being very uneven and of a low quality.

I have recently removed quite a bit of soil from the front garden which I hope to use to level the rear garden. Is it best to hire a tiller and rotovate the whole area and level off and then use grass seed or is there a better way ?

What's the best time of year to do it ?