Sintaxis de MySQL
update [table_name] set [field_name] = replace([field_name],'[string_to_find]','[string_to_replace]');
Para mover wordpress a otro sitio web
update wp_posts set post_content = replace(post_content,'sitioviejo.com','sitionuevo.com')
update wp_posts set guid = replace(guid,'sitioviejo.com','sitionuevo.com')
update wp_options set option_name = replace(option_name,'sitioviejo.com','sitionuevo.com')
update wp_options set option_value = replace(option_value,'sitioviejo.com','sitionuevo.com')