I want to delete one page using Pages

The default Pages word processing document does not permit removing thumbnails (e.g. a page) without whacking all pages in the document. An optional Page layout document, where each thumbnail is its own discrete section, allows one to delete that individual section/page using the thumbnail secondary menu.

In a word processing layout document, you must select all text on the page to remove, and press backspace twice — once to whack the page text, and once more to delete the hidden page break.

You could just highlight and delete everything on that page...