To delete a page, go into edit mode on the page you want to delete, and click the Organise pages button on the toolbar, as shown in figure 1.

Figure 1. the organise pages button

This will open the page organisation window, as shown in figure 2.

Figure 2. the page organisation window

Click Delete this page and confirm that you want to delete the page. After the page has been deleted, you will be taken to the parent page.