There is no actual withdrawal procedure from the UN, and as such, international law dictates that a party may withdraw from a treaty with no withdrawal provisions only if an unforeseeable change in circumstances occurs. The UN charter wrote it specifically without a withdrawal charter, keeping in mind the events that occurred following the Japanese withdrawal from the League of Nations
It will not be feasible for the United States to withdraw from the United Nations.The United States was one of the founding members as well as one of the biggest current ones.Without the United States the United Nations would probably cease to exist and much more chaos would break out throughout the world.
The United Nations is such a carefully ingrained part of the international political landscape that it would be very difficult for any of the major powers to extricate themselves from it. This applies to the United States as well. I don't think that it would be feasible to withdraw without a ton of political backlash.