Promote & Demote users through user.php

functions.php

/* Update the users role inside the users page with a fucking button! */

/** Manage custom columns on instances of 'WP_List_Table' */
add_action('init', 'my_setup_custom_columns', 110, 0);
function my_setup_custom_columns(){

    /** Manage columns on the WP_Users_List_Table */
    add_filter('manage_users_columns', 'my_add_custom_columns');

    /** Populate additional columns on the WP_Users_List_Table */
    add_action('manage_users_custom_column', 'my_fill_custom_columns_return', 10, 3);

}

/**
 * Add additional custom columns to the list table views in the admin area
 *
 * @param required array $columns   The columns that currently exist
 */
function my_add_custom_columns($columns){

    /** Grab the page that is currently being viewed */
    global $pagenow;

    /** Users specific columns (http://www.blog.com/wp-admin/users.php) */
    if($pagenow === 'users.php') :

        $new_columns['my-change-user-role'] = __('Change Role');

    endif;

    $columns = $columns + $new_columns;

    return $columns;

}

/**
 * Fill the custom columns by returning data
 *
 * @param required string $column_value The current column value (in this case 'null' since the columns are new)
 * @param required string $column_name  The name of the column to return data for
 * @param required integer $object_id   The ID of the curent object to fill the column for
 * @return string $column_value         The value to fill the column with
 */
function my_fill_custom_columns_return($column_value, $column_name, $object_id){

    switch($column_name) :

        /**
         * ID (the ID of the current object)
         */
        case 'my-change-user-role' :

            $user = get_userdata($object_id);
            $role = $user->roles[0];

            if($role === 'partner') :
                $column_value = '<span user-id="' . $object_id . '" new-role="prospect" class="change-user-role">Downgrade to a prospect</span>';
            elseif($role === 'prospect') :
                $column_value = '<span user-id="' . $object_id . '" new-role="partner" class="change-user-role">Upgrade to a Partner</span>';
            else:
                $column_value = '&#8212;';
            endif;

            break;

    endswitch;

    return $column_value;

}

/**
 * Change the role of a given user
 */
add_action('wp_ajax_change_user_role', 'my_update_user_role');
function my_update_user_role(){

    /** Update the user role */
    $args = array(
        'ID'    => $_POST['user_id'],
        'role'  => $_POST['new_role']
    );
    $result = wp_update_user($args);

    /** Check whether or not the update was successful */
    if(is_wp_error($user_id)) :
        $message = 'An unexpected error occurred, please try again.';
        $url = false;
    else :
        $message = 'success';
        $url = admin_url('users.php');
    endif;

    $return = array(
        'message'   => $message,
        'url'       => $url
    );
    echo json_encode((object)$return);

    wp_die(); // This is required to terminate immediately and return a proper response
}

// Put Javascript file on Users page
function upgrade_user($hook) {
    if ( 'users.php' != $hook ) {
        return;
    }
    wp_enqueue_script( 'upgrader', get_template_directory_uri() . '/library/js/upgrade_user.js' );
}
add_action( 'admin_enqueue_scripts', 'upgrade_user' );

/* Add a quick style to the users.php page */
add_action('admin_head', 'upgrader_user_button');
function upgrader_user_button() {
  echo '<style>
    .change-user-role{
		background: firebrick;
		border: medium none;
		border-radius: 2px;
		color: white;
		cursor: pointer;
		display: inline-block;
		font-style: normal;
		font-weight: normal;
		outline: medium none;
		padding: 7px 14px;
		text-align: center;
		text-decoration: none;
		text-indent: 0;
	}
	/* If button is "Upgrade to partner" - we\'ll give it something to shout about*/
	.change-user-role[new-role="partner"] {
	    background: limeGreen;
	}
	
    .wp-list-table.users .manage-column.column-my-change-user-role {
      width: 150px;
    }
    .wp-list-table.users span.change-user-role {
      color: #0074A2;
      cursor: pointer;
    }
    .wp-list-table.users span.change-user-role:hover {
      color: #2EA2CC;
    }

  </style>';
}

upgrade_user.js

jQuery(function($){

    $(document).ready(function(){
        updateUser.init();
    });

    var updateUser = {

        /**
         * Psuedo constructor
         */
        init : function(){

            this.userChangeRoleButtons = $('.wp-list-table.users span.change-user-role');   // Grab all instance of the buttons to change the user role
            this.createEvents();                                                            // Create the events to be handled by this object

        }, // init

        /**
         * Create the events that are to be handled by this object
         */
        createEvents : function(){

            var t = this;   // This object

            /**
             * Handle clicks of the change user role buttons
             */
            this.userChangeRoleButtons.on('click', function(e){

                t.changeRole($(this));

            });

        }, // createEvents

        /**
         * Updates the user role as required
         */
        changeRole : function(clicked){

            var t               = this, // This object
                user_id         = clicked.attr('user-id'),
                new_role        = clicked.attr('new-role');

            var data = {    // The data object to pass to the AJAX request
                action:     'change_user_role',
                user_id:    user_id,
                new_role:   new_role
            };

            /** Make the AJAX request to update the download count */
            var action_jqxhr = $.post(ajaxurl, data, function(response){

                /** Parse the JSON response */
                var obj = JSON.parse(response);

                /** Ensure that there were no errors and update the 'Change role' button text */
                if(obj.message.indexOf('error') === -1){    // There was no error, redirect the user back to this page

                    top.location.replace(obj.url);

                } else {    // There was an error, tell the user about it

                    alert(obj.message); // Show the error to the user

                }

            }).fail(function(){ // There was an AJAX error...
                alert('An unexpected error occured, please try again.');
            });

        } // changeRole

    };

});