I see that you have a lot of content to be deleted and I have tagged this thread for Staff. They can can empty the whole blog for you and that will remove all data including posts, pages, tags, categories, comments, and uploaded files. Once deleted, the data cannot be recovered.
If you are sure you want Staff to proceed, then post again to this thread to:
(1) confirm the URL of the blog you want Staff 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.