How to remove information from the footer of the website?

For pages connected to a master page, a modification to the Footer module of your master page will modify all connected pages.

For pages that are not connected to a master page, you will have to make inactive the information in each page's footer module.

The use of a master page is very useful for this kind of mass modification. If you haven't already done so, it might be interesting for you to review your use of master pages for your site.