backend - how much customization is available?

In WordPress, the backend development services are used to define the admin area of the website where you create content, install plugins, and manage design settings.

hello,
in the backend of this, are there options to show or hide the various products shown in the demo? For example, I would only want posters, business cards and cards shown from those in the demo. Are the posters customizable size-wise? for example, could I have an 11x17 one and an 8.5x11 one?
thanks