Move them to Zimbabwe.
Seriously, I have long thought the UN headquarters should rotate every five or six years from one continent to another, and should each time be located in the most contentious area on the continent. That way the UN would learn to shit or get off the pot in a hurry. They would learn the real meaning of negotiating. Meanwhile, since their pampered membership like to eat and sleep well, and pass water and gas in peace, the host country would benefit in terms of a substantial development of a service industry which would perhaps remain even after the UN moved on. And if the temporary host country had little else to make it attractive, they could at least gussy-up the former UN headquarters and the former international school if idiots had not yet blown up either or both or religious or ethnic grounds!
And it would get those ruddy and rank UN bastards out of New York City, which could then allow private enterprises to tear down that insignificant and architecturally- challenged edifice and replace it with something of vastly greater economic and cultural value in about 18 months, or maybe 8 months.
"UN: a movable feist, fist, fest, feast, fossil, fart(oops), should have said phlegm!"