user role

functions.php

add_action( 'woocommerce_order_status_completed', 'wpglorify_change_role_on_purchase' );

function wpglorify_change_role_on_purchase( $order_id ) {

// get order object and items
$order = new WC_Order( $order_id );
$items = $order->get_items();

$product_id = 56; // that's a specific product ID

foreach ( $items as $item ) {

        if( $product_id == $item['product_id'] && $order->user_id ) {
            $user = new WP_User( $order->user_id );

            // Remove role
            $user->remove_role( 'subscriber' ); 

            // Add role
            $user->add_role( 'editor' );
        }

}

}