Taking up the old lawn

Hi, we've recently moved into a new property where the garden hasn't been touched in years. It's extremely lumpy and bumpy and slopes down towards the back. The grass is dying and unruly and filled with brambles.
We want to take the lawn up and returf it starting from scratch. What's the best way please? Our thoughts so far are:
1. Use a turf cutter, cut it all up and use some excess turf to bulk out the uneven layer at the back of the garden so its level and skip the rest
2. Rotatvate the lawn and returf it - would the lawn need a treatment of weedkiller on it first?
Any advice on the easiest way to do this would be a great help - thanks

 

I'd blitz it with roundup first. Give that a couple of weeks to work, then trim any long/overgrown stuff down a bit (not fully) and blitz again. Give it another two weeks. If anything is still alive, then blitz and wait again.

Only when you're sure it's all dead, then I'd clear it and level it. But don't use old turf to fill any significant dents. It won't work. You'll never get it perfectly level and if you do, it will sink over time as turf has more organic matter to rot away than the soil does, so it will sink at different rates in different places.