If you have a blog on WordPress.com and want to back it up just do the following:
1.) Login to WordPress.com. Click “My Blogs”, then on Your Blog Name and “Dashboard”.
2.) On the left scroll down and click “Tools” and then “Export”.
3.) There will be two options. Make sure you click the one that says “Export” and has the cost of FREE.
4.) To backup everything make sure each drop down option is set to “All” and then click “Download Export File”.
5.) Make sure the download completes and you save it somewhere that you will remember. Now you will have a backup of your blog, just in case.