Posted: 21/03/2017 at 14:27
Hello and welcome.
There are grinding machines that can take out tree stumps. A local tree surgeon will have one and you may even be able to hire one form a good DIY or tool hire store. That would be the first thing to do and then you'd need to dig over the whole area and rake it level so you can re-sow a lawn or lay turves.
However, it is usually advised that for the first year in a new garden you just do basic maintenance so you can see what, if anything, grows. Many plants are only just emerging after their winter hibernation and you may lose treasures if you dig it all up now.
You can hire turf cutters to strip off the top layer of grass. You then roll or stack it grass to grass, soil to soil, in a corner where it will rot down to make lovely soil. Alternatively, you could spray the grass with a glyphosate based weedkiller - as long as you are careful to read the instructions and keep it away form water - and then you can dig over the grass when it's dead.
Before laying new turves or sowing new seed, scatter a good dressing of something like pelleted chicken manure or blood fish and bone on the soil and rake it in. This will improve fertility for your new lawn. Think also about where you may want to create beds, seating areas, composting areas and storage areas so you can lay those out - mark with dry sand or a hose-pipe or string - so you can get a good estimate of how much seed or turf you will need and thus have less waste.