Yes you can do that.
You can quickly remove your contents by deleting them in bulk.
bulk delete images & media http://en.support.wordpress.com/media/deleting-files/#bulk-deletion
bulk delete posts > http://en.support.wordpress.com/posts/edit-posts-screen/#bulk-edit
bulk delete pages > http://en.support.wordpress.com/pages/edit-pages-screen/#bulk-edit
Here's how to permanently delete Trash >
If you have tonnes of content Staff can empty the whole blog for you. That will remove all data including posts, pages, tags, categories, comments, and uploaded files and once deleted, the data cannot be recovered.
If you are sure you want Staff to proceed, then type modlook into the tags in the sidebar for Staff attention and post again to this thread to:
(1) confirm the URL of the blog you want them to empty;
(2) confirm that you know content deletion is irreversible.
IMPORTANT NOTE: Deleting blog content does not remove it from the SERPs (search engine page results). Google and Bing only clear their caches of deleted indexed content that produces a 404 (page not found) every 3 - 6 months.