Frequently when using the AutoNav plugin, the Hierarchical Pages Widget or other plugins which depend heavily on nested pages and on attachments to pages and posts, one finds that a page, or an attachment, needs to be moved. Here are two plugins to handle these tasks easily:
Pagemash lets you move pages up, down, in, out, and around your hierarchy with the mouse. Amazingly easy.
Change Attachment Parent is an easy way to reset the parent page or post for any attachment, right on the attachment’s Edit screen in the Media Library. You do need to know the new parent’s ID, though.
Suggestion: If you have a large site and don’t want to look up the parent ID (or don’t know how to look up the parent ID), you can just change the attachment parent to zero. Then you can go through the regular attachment form to find the right page.
This is how I tell my clients to do it, as they’re not savvy about things like post/page IDs.