We cannot do this for you: you have to act.
Please deal with the site(s) first.
To delete a WordPress.COM hosted blog you must be logged in as Admin under the exact same username account that registered the blog to navigate to Dashboard > Tools > Delete Site. The guide is here http://en.support.wordpress.com/delete-site/
https://wordpress.com/settings/delete-site/NAME_OF_BLOG.wordpress.com
*Replace "NAME_OF_BLOG" with the actual name of the blog in the URL above.
If you are not logged in under the correct username account then clear your browser cache https://en.support.wordpress.com/browser-issues/#clearing-your-browser-cache and cookies https://en.support.wordpress.com/browser-issues/#clearing-wordpress-com-cookies prior to logging into another account
If the log-in information is lost you need to visit https://en.wordpress.com/wp-login.php?action=lostpassword
Read also: Account Recovery https://en.support.wordpress.com/account-recovery/
Be aware that deleted blog URLs are not recycled, regardless of who registered and deleted them and no exceptions are made except for the one stated here http://en.support.wordpress.com/recycling-blog-names/
Other options
Provided you are logged in as Admin under the exact same username account that registered the site, to change blog visibility to Private go to > Dashboard > Settings > Reading scroll to Blog Visibility and choose option 3. See the guide here http://en.support.wordpress.com/settings/privacy-settings
To empty site content and keep the URL see here https://en.support.wordpress.com/empty-site/
You can keep the URL and delete the content.
re: changing a .wordpress.com address
We cannot edit any blog URLs. If you want to change the .wordpress.com blog address ie. the URL starting with http:// then you must be logged in as Admin under the exact same username account that registered the blog to do that and the URL you desire must be available. If so, then you can change the URL by using the guide http://en.support.wordpress.com/changing-blog-address/ Then all the content will be the same only the URLs will change and nothing else.
Be sure to locate the correct page http://en.support.files.wordpress.com/2011/01/dashboard-e1371648470893.png
Changing a URL is meant to be a permanent and irreversible act. No changed or deleted blog URLs are recycled here, regardless of who registered and deleted them and the only exceptions are made are for URLs that were deleted 2 or more years ago
http://en.support.wordpress.com/recycling-blog-names/
You can simply switch themes. https://en.support.wordpress.com/themes/#switch-themes
To transfer the site to another username account provided that username account has first been added as an official user of the blog https://en.support.wordpress.com/user-roles/#adding-users-to-your-site with Admin status. https://en.support.wordpress.com/user-roles/#administrator
http://en.support.wordpress.com/moving-a-blog/#transferring-your-blog-to-another-user-or-account
Here's how to deactivate your account:
Although username accounts are not deleted, so you cannot be impersonated and have your reputation affected by anyone registering the same username in the future, there are steps you can take that amount to removing all personal information and result in leaving only a throwaway email address behind. http://en.support.wordpress.com/deleting-accounts/
1. You can go to My Account->Edit Profile at https://wordpress.com/me/account and remove all data except the account name and an email address. Create a throwaway email address and change the account email to that throwaway address. This only leaves the username behind.
2. To unsubscribe from email sent to you from WordPress.com, go here and click on “Block all subscription emails from WordPress.com”:
https://wordpress.com/settings/notifications/
3. To ensure the account is locked up tightly, visit this site, generate a password of 15-20 characters, and change the account password to it:
http://www.thebitmill.com/tools/password.html
4. To hide your Gravatar profile, login and on the bottom right hand corner of your Gravatar profile page you will find a "hide" button visible only to you that you can click. http://en.gravatar.com/support/profile-privacy
IMPORTANT NOTE: Deleting blogs and/or blog content or making the site private does not remove indexed content from the SERPs (search engine page results) and we cannot help with that. Google and Bing only clear their caches of deleted indexed content that produces a 404 (page not found) every 3 - 6 months. To completely remove an entire page from Google search results after it produces a 404 (page not found):
https://support.google.com/webmasters/answer/6332384?hl=en&ref_topic=1724262&vid=0-635749429504660340-12158368555624983465&rd=1