1. Before you start take a backup of your website files and database.
  2. Deactivate all your plugins.
  3. Edit wp-config.php and add the following line above /* That’s all, stop editing! Happy blogging. */
    /* Multisite */
    define( 'WP_ALLOW_MULTISITE', true );
  4. Open your WordPress Dashboard
  5. Click Tools > Network Setup
  6. Choose a Network Title and click Install
  7. Follow the on-screen instructions and add the code blocks to your wp-config.php and .htaccess files.
  8. Log into your WordPress Dashboard
  9. Click Plugins and re-activate your Plugins
  10. From the top menu, click My Sites > Dashboard to start managing your WordPress Multisite Network.