from a photo book in Photos
Are you using Photos or iPhoto? You mention both applications.
If you are using Photos, follow these instructions: https://support.apple.com/guide/photos/work-with-pages-pht6e15c151/mac
Delete a page from a book: Click the page to select it and press Delete, or click the Add Page button in the toolbar, choose Remove Page, then click Continue. You can also Control-click the page, choose Remove Page, then click Continue.
If you are using iPhoto '11, version 6.0.5, follow these instructions: https://help.apple.com/iphoto/index.html#pht6e15c151
Press the Control key while you click the page that you want to delete, and then choose Remove Page from the shortcut menu.