how to update morph associations laravel code example

Example: laravel polymorphic model

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class Image extends Model
{
    /**
     * Get the owning imageable model.
     */
    public function imageable()
    {
        return $this->morphTo();
    }
}

class Post extends Model
{
    /**
     * Get the post's image.
     */
    public function image()
    {
        return $this->morphOne('App\Image', 'imageable');
    }
}

class User extends Model
{
    /**
     * Get the user's image.
     */
    public function image()
    {
        return $this->morphOne('App\Image', 'imageable');
    }
}