You can remove pages and blog posts through the "Tools" option on the right side of the page. If you do not see the option to remove a page under the tool menu, contact your space administrator for access.
Pages are not permanently deleted. Instead, these pages are moved to the trash. Space administrators can permanently remove pages by "purging" the trash and can restore a page under the administration screens.
Attachments are deleted with a page, but child pages are not. Child pages are instead moved to the root of the space, and can be reorganized under the "Pages" screen.