Can I update the theme and plugins (used in your readymade website) manually whenever there is a new update available for them?

Yes, you can do. However, before updating the WordPress theme and plugins, we recommend you take your website backup once! And for your kind information, we have used our own child themes to customize the look and feel of these readymade websites. Hence, whenever you update the main theme and plugins in these readymade websites, the sites look and feel will not be disturbed!