Hi Hong Jail,
Happy New Year! And thank you for your purchase.
1: Which options and text do you want to change? Please let us know in detail.
2: Current multi-currency & multi-language menu are just static html to show demo.
If you want to set the real menu content, you need to install some plugins.
Multi-language menu is compatible with WPML, so if you install and set your languages, current static language menu content will be replaced with your set languages.
And multi-currency menu is compatible with "WOOCS - WooCommerce Currency Switcher" plugin.
If you install this plugin, you can set your currencies.
If you want to remove these menus, you can disable these on lorada theme option panel->header->other elements like screenshot.
3: User registration page will work well normally. If it doesn't work, please enable the "anyone can register" option on wp-admin->settings like screenshot.
If you have any other questions, please feel free to contact us without hesitation.
Best Regards, C-Themes