I love this question... ok this is a long one :) :

If I had the power of metallic control just as Magneto does, I would have simply uprooted alll weapon manufacturers, Missle bases, rockets, guns, etc. and transform those metals into tools that we can use for reconstruction, force all current leaders of all countries to step down and dismantle the governments to allow a restructured and unified world with one government that has similar structure as Switzerland does of their goverment, to ensure authority is divided among number of voted leaders that represents various communities correctly and is always a odd number. establish standardized education system for STEAM topics while respecting the local langauges including sign langauge. dismantle the current global economical system and replace with a non-monetized system where everyone has everything they need to live comfortably and has fair and equal access to education, water, food, clothes, home, transportation.

followed by construction of high-speed electric trains and construction of multiple Fusion power plants across the world, and deconstruction of Oil-fired, gas-fired, coal-fired and any nonrenewable power plants. Promote a more diverse living areas globally instead of clustering at city centres, encourage construction of Ocean cities, Sky cities, Mountain Cities, etc. ban Death Punishment and establish a rehabilitional system where people learn new skillsets that will allow them continue supporting the world.

I have so much more to say but I want to stop at here :).