In blogspot there is no facility to back up or download all your post and comments left by readers as in Wordpress blog. However there are some third party utilities to helps you, among them Blogger backup is the most suitable for this purpose. This utility saves all your Blogger posts to the hard disk and can easily restore them in case you accidentally delete your blog or some of the posts.
After installation, just login with your Blogger account and select your blog to save locally. You can either save all your posts in to a single file or let the software create new file per blog entry. It can also backup reader comments.
If you want to restore any of your post from the hard disk that are deleted from your blog, just hit the ‘Restore Posts’ button, select the post and they will be back online.
The application follows the incremental backup style, that is, if you run the Blogger backup again after a week, it restores the posts that published in that period, not the entire posts. [Source] Download Blogger Backup