Use the link. Then choose to ‘downgrade’, i.e. only delete your Google Plus account, or delete your complete Google account.
URLS:
http://plus.google.com
https://plus.google.com/u/0/downgrade/
Please note that AccountKiller.com is not associated with the business listed on this page. AccountKiller provides easy-to-understand instructions and guides on how to cancel charges and relationships from the list of businesses on our site, we have no affiliation with these businesses.