When only one page is present, it cannot be deleted.
To delete a page within My Folder, do the following:
Select My Folder in the navigation area.
Locate the Custom Pages portlet. Initially, this is located on My Page. If the portlet has been removed, add it to the page.
Locate the page you want from the list in the Custom Pages portlet. Then select the Delete action.
The Delete Page dialog appears showing the selected page.
Click Delete.