Extension methods for easily reordering an item in a list.

RXListReordering.cs

using UnityEngine;
using System;
using System.Collections.Generic;

public static class RXListReordering
{
	public static bool CanReorder<T>(this List<T> items, T item, int dir)
	{
		var index = items.IndexOf(item);
		if(index == -1) return false;
		var newIndex = Mathf.Clamp(index + dir, 0, items.Count-1);
		return (index != newIndex);
	}

	public static bool Reorder<T>(this List<T> items, T item, int dir)
	{
		var index = items.IndexOf(item);
		var newIndex = Mathf.Clamp(index + dir, 0, items.Count-1);

		if(index != newIndex) //did index change
		{
			items.RemoveAt(index); //remove the item from its previous location
			if(newIndex > index) index++; //because the indices will change 
			items.Insert(newIndex,item);
			return true;
		}
		else 
		{
			return false;
		}
	}
}

Usage:
myList.Reorder(someItem,-1) to move an item up,
myList.Reorder(someItem,1) to move an item down.

Use myList.CanReorder(someItem, -1) to find out if you can move an item upwards.
Use myList.CanReorder(someItem, 1) to find out if you can move an item downwards.