First, open your WordPress dashboard for the site in question. At the upper left hand corner of your screen, click “Dashboard.” From there, click the “My Blogs” link. That will bring up a list of all of your active WP sites. You should see nightsquest.wordpress.com in the list.
The link to “Change Blog Address” does not appear until you hover your cursor over the existing address of your blog. Once it’s there, you should be able to click the option to change the URL – it will take you to a page with some warnings you should read closely, but it’s there that you can actually make the change.