To remove the captcha field from the contact form, it requires to do some changes in custom-function.php file.
If you want to remove captcha field, please send your website URL and WordPress admin login details at [email protected] so we can customize the code as per your requirement.
Alternately if you don’t want to use this default contact form, you can use Contact Form 7 WordPress plugin. Just create a form and use shortcode in contact page.