Sam Hughes has created a nice “must read’ document for any would be plotters against the existence of the Earth. He gives different Earth destroying techniques along with the feasibility of each technique. In short, it’s not easy.
If total human genocide is your ultimate goal, you are reading the wrong document. There are far more efficient ways of doing this, many which are available and feasible RIGHT NOW. Nor is this a guide for those wanting to annihilate everything from single-celled life upwards, render Earth uninhabitable or simply conquer it. These are trivial goals in comparison.
This is a guide for those who do not want the Earth to be there anymore.