winfrithwebsite on "One email linked to two sites"

I must be misunderstanding something as i read that you have to have a different email for each website/blog. I seem to have two websites/blogs linked to the same email. To be specific ridgewaysingersandband.wordpress.com and winfrithnewburgh.org.uk both seem to link to the same email. I now want to change the email for one (not both) of them and cannot see how to do it.